Inactivation of calcium-activated chloride conductance in Xenopus oocytes: roles of calcium and protein kinase C

Abstract

Inactivation of Ca2(+)-induced Cl- currents was studied in Xenopus oocytes using the two-electrode voltage-clamp technique. In oocytes permeabilized to Ca2+ by treatment with the ionophore A23187, Ca2+ influx caused by the addition of 2.5-5 mM Ca2+ to the extracellular solution elicited Cl- currents consisting of two components: a fast, transient one (Ifast) and a slow one (Islow). In response to a subsequent application of the same dose of Ca2+, Ifast and Islow were reduced (inactivation phenomenon). The inactivation did not depend on the direction of current flow, but did depend on the duration of the first exposure to Ca2+. The extent of inactivation of Ifast was more significant than that to Islow. Both Ifast and Islow fully recovered from inactivation in less than 30 min. Intracellular injections of 100-400 pmol CaCl2 evoked large inward currents but did not reduce the amplitude of currents evoked by Ca2+ influx. The activator of protein kinase C, beta-phorbol dibutyrate, caused full inhibition of Ifast without any change in Islow. H-7 (1,5-isoquinolinesulfonyl-1,2 methylpiperazine), an inhibitor of protein kinases, strongly reduced the extent of inactivation. Our results suggest that elevation of intracellular Ca2+ by Ca2+ influx through the plasma membrane causes inactivation of the Ca2(+)-dependent Cl- conductance via activation of a Ca2(+)-dependent protein kinase, possibly protein kinase C, whereas Ca2+ arriving at the membrane from inside the cell does not initiate the processes leading to inactivation.

Homologous Desensitisation of the Mouse Leukotriene B₄ Receptor Involves Protein Kinase C-Mediated Phosphorylation of Serine 127

“…Traces recorded from non-injected oocytes treated with PMA showed a reduction in the fast initial spike current, but the sustained current was still observed (data not shown). This finding indicates that the fast Ca 2+ -activated Cl --current component was inhibited by PMA treatment, whereas the slowly progressing Cl --current component was unaffected, in accordance with previously published data [28]. Thus, based on these data, it cannot be excluded that part of the effect of PMA could reflect an effect of PKC on the Cl -channels responsible for the initial fast current; however, it is unlikely that the PMA treatment affects the Cl -channels responsible for the prolonged Cl -current.…”

Computational Model of the Insect Pheromone Transduction Cascade

“…However, in the latter case, we studied the hypothesis of a feedback inhibition via PKC* [63]. We found that both regulations are not essential (Figure 5B).…”

A Common Mechanism Underlies Vertebrate Calcium Signaling andDrosophilaPhototransduction

“…Although ionomycin renders the plasma membrane somewhat leaky to Ca 2ϩ , in Xenopus oocytes this effect is very small, and the resulting Ca 2ϩ influx is very slow and cannot be confused with the robust effect of store depletion caused by ionomycin or other Ca 2ϩ ionophores (Boton et al, 1990). Suppression in InsP 3 -Ftreated cells reached 77 Ϯ 4.8% (n ϭ 14), and the recovery reached 50% after 28 min (n ϭ 8).…”

“…However, whereas the initial transient reflects only Ca 2ϩ release, the oscillations reflect release and reuptake of Ca 2ϩ into the InsP 3 -sensitive stores (Lechleiter et al, 1991;Jafri et al, 1992). Also, the initial transient and oscillations have different properties, probably reflecting Ca 2ϩ release from different pools (Gillo et al, 1987) or different gating mechanism of I C l,C a (Boton et al, 1990). When experiments similar to those of Figure 1 A were undertaken without external Ca 2ϩ the prolonged current and oscillations were very similar to those of Figure 1 A (n ϭ 16).…”