Williamson replies:

Williamson, P. G.

doi:10.1038/296611b0

Cited by 22 publications

(14 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Assuming that all the current injected into the cytoplasm-enriched fragments was carried by Ca2 +, the total load into the cytoplasm-enriched fragments per pulse would be 0.15 nmol Ca2+. Chara cells were observed to buffer the calcium rise during an action potential to -6% of the peak value almost instantaneously (Williamson and Ashley, 1982). From this estimate of buffer capacity, a 60 s Ca2+ pulse (500 nA) into an average cytoplasmic volume of 4 Al would increase the resting concentration of cytoplasmic free calcium from 0.2 /tM (Williamson and Ashley, 1982;Miller and Sanders, 1987) to 2.4 ItM.…”

Section: Discussionmentioning

confidence: 98%

“…The fact that Ca2+ injection into Chara fragments did not affect the transmembrane voltage may be related to the high Ca2+ buffer capacity of the cytoplasm (Brinley et al, 1977;Williamson and Ashley, 1982). Assuming that all the current injected into the cytoplasm-enriched fragments was carried by Ca2 +, the total load into the cytoplasm-enriched fragments per pulse would be 0.15 nmol Ca2+.…”

Section: Discussionmentioning

confidence: 99%

“…Chara cells were observed to buffer the calcium rise during an action potential to -6% of the peak value almost instantaneously (Williamson and Ashley, 1982). From this estimate of buffer capacity, a 60 s Ca2+ pulse (500 nA) into an average cytoplasmic volume of 4 Al would increase the resting concentration of cytoplasmic free calcium from 0.2 /tM (Williamson and Ashley, 1982;Miller and Sanders, 1987) to 2.4 ItM. The real increase is likely to be even smaller, because an injection current is not carried by Ca2+ only (Purves, 1981).…”

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Raising the intracellular level of inositol 1,4,5-trisphosphate changes plasma membrane ion transport in characean algae.

1990

View full text Add to dashboard Cite

Inositol 1,4,5‐trisphosphate (InsP3) was introduced into the cytoplasm of characean algae in two different ways: (i) by iontophoretic injection into cytoplasm‐enriched fragments from Chara and (ii) by adding InsP3 to the permeabilization medium of locally permeabilized cells of Nitella. In both systems this operation induced a depolarization of the membrane potential, ranging from a few mV to sequences of action potentials. The effect of InsP3 on locally permeabilized Nitella cells was abolished when InsP3 was added together with 30 mM EGTA. When inositol 1,4‐bisphosphate or myo‐inositol were substituted for InsP3 in this system, there was no change in the membrane potential. On the other hand, increasing the free Ca2+ concentration in the permeabilization medium induced, in a similar fashion to InsP3, action potentials. Similarities between InsP3 and Ca2+ action were also observed upon injection into Chara fragments. Both injections increased an inward current. In the first few seconds after injection the current/voltage characteristics of the InsP3‐induced current resembled those of the Ca2(+)‐sensitive current. Subsequently, differences between the InsP3‐ and Ca2(+)‐induced phenomena became apparent in that the InsP3‐induced current continued to increase while the Ca2(+)‐induced current declined, returning to the resting level. Our results suggest that these plant cells contain an InsP3 sensitive system that, under experimental conditions, is able to affect membrane transport via an increase in cytoplasmic free Ca2+.

show abstract

Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Raising the intracellular level of inositol 1,4,5-trisphosphate changes plasma membrane ion transport in characean algae.

1990

View full text Add to dashboard Cite

show abstract

“…The plasma membrane of characean algae is electrically excitable (for review see [1]). It is generally accepted that depolarization beyond a critical threshold voltage causes an increase in the concentration of free cytoplasmic Ca 2 , [Ca 2 ] cyt [2,3]. This elevation is thought to activate Ca 2 -dependent Cl 3 channels giving rise to further depolarization of the membrane voltage (V m ) (for review see [4]).…”

Section: Introductionmentioning

confidence: 99%

Calcium release from InsP₃‐sensitive internal stores initiates action potential in Chara

1999

View full text Add to dashboard Cite

Neomycin and U73122 are known to suppress inositol 1,4,5-trisphosphate (InsP3) production by inhibition of phospholipase C. We studied the effects of these inhibitors on the excitatory currents, Iex, in Chara corallina under voltage-clamp conditions. Computer simulations of the experimental effects by a minimum model for the excitatory reaction pathway allow the assignment of the inhibitory effects to one specific reaction step, i.e. the release of Ca2+ from InsP3-sensitive internal stores. In contrast, the inhibitory effect of La3+ on Iex suggests inactivation of Cl- channels. Furthermore, ryanodine-sensitive Ca2+ stores seem to be irrelevant for electrical excitation in Chara.

show abstract

“…The pre-depolarizing pulses necessary to fully recruit voltage-dependent calcium channels in carrot cells are unlikely to occur in normal physiological conditions. Nevertheless, depolarizations to potentials of up to +50 mV have been reported in plant cells (Williamson and Ashley, 1982). Furthermore, initial activation of higher plant voltage-dependent Ca2+ channels (Thuleau et al, 1994) can also transiently depolarize the plasma membrane to positive potentials due to the ¢ 1000-fold gradient of Ca>2 ions across the plasma membrane.…”

Section: Discussionmentioning

confidence: 99%

Recruitment of plasma membrane voltage-dependent calcium-permeable channels in carrot cells.

et al. 1994

View full text Add to dashboard Cite

Numerous biological assays and pharmacological studies have led to the suggestion that depolarization‐activated plasma membrane Ca2+ channels play prominent roles in signal perception and transduction processes during growth and development of higher plants. The recent application of patch‐clamp techniques to isolated carrot protoplasts has led to direct voltage‐clamp evidence for the existence of Ca2+ channels activated by physiological depolarizations in the plasma membrane of higher plant cells. However, these voltage‐dependent Ca2+ channels were not stable and their activities decreased following the establishment of whole‐cell recordings. We show here that large pre‐depolarizing pulses positive to 0 mV induced not only the recovery of Ca2+ channel activities, but also the activation of initially quiescent voltage‐dependent Ca2+ channels in the plasma membrane (recruitment). This recruitment was dependent on the intensity and duration of membrane depolarizations, i.e. the higher and longer the pre‐depolarization, the greater the recruitment. Pre‐depolarizing pulses to +118 mV during 30 s increased the initial calcium currents 5‐ to 10‐fold. The recruited channels were permeable to Ba2+ and Sr2+ ions. The data suggested that voltage‐dependent Ca(2+)‐permeable channels are regulated by biological mechanisms which might be induced by large pre‐depolarizations of the plasma membrane. In addition, this study provides evidence for the existence in the plasma membrane of higher plant cells of a large number of voltage‐dependent Ca2+ channels of which a major part are inactive and quiescent. It is suggested that quiescent Ca2+ channels can be rapidly recruited for Ca(2+)‐dependent signal transduction.

show abstract

Williamson replies:

Cited by 22 publications

References 6 publications

Raising the intracellular level of inositol 1,4,5-trisphosphate changes plasma membrane ion transport in characean algae.

Raising the intracellular level of inositol 1,4,5-trisphosphate changes plasma membrane ion transport in characean algae.

Calcium release from InsP₃‐sensitive internal stores initiates action potential in Chara

Recruitment of plasma membrane voltage-dependent calcium-permeable channels in carrot cells.

Contact Info

Product

Resources

About

Williamson replies:

Cited by 22 publications

References 6 publications

Raising the intracellular level of inositol 1,4,5-trisphosphate changes plasma membrane ion transport in characean algae.

Raising the intracellular level of inositol 1,4,5-trisphosphate changes plasma membrane ion transport in characean algae.

Calcium release from InsP3‐sensitive internal stores initiates action potential in Chara

Recruitment of plasma membrane voltage-dependent calcium-permeable channels in carrot cells.

Contact Info

Product

Resources

About

Calcium release from InsP₃‐sensitive internal stores initiates action potential in Chara