Protein kinase A increases availability of calcium channels in smooth muscle cells from guinea pig basilar artery

Abstract

We studied single Ca2+ channels in smooth muscle cells from the basilar artery of the guinea pig using conventional patch-clamp techniques. With 40 mM or 90 mM Ba2+ as the charge carrier, a 23-pS inward current channel was observed in 46/187 cell-attached patches studied without the dihydropyridine, BAY K8644, in the pipette solution. At 0 mV, this channel exhibited short and long openings with time constants of 1.03 and 3.65 ms, respectively. The probability of channel opening was voltage dependent with half-activation occurring at +9.9 mV. In 14/26 patches tested, addition of 8-bromo-cyclic adenosine monophosphate (8-Br-cAMP) to the bath increased the probability of opening at -10 mV by a factor of 2.6, from 0.0272 +/- 0.0429 to 0.0695 +/- 0.0788 (P < 0.01, paired t-test). Mean data from five patches fit to a Boltzmann function indicated that at positive potentials, the probability of opening increased by a factor of 1.7, from 0.352 to 0.600, whereas the voltage dependence, the number of channels, the number of open states, the time constants of the open states, and the proportion of time spent in each open state were unchanged. When BAY K8644 was added to the pipette solution, the 23-pS channel was observed in nearly all patches (62/66), but the voltage dependence of activation was shifted -15.3 mV compared to control. In some patches studied with 90 mM Ba2+, a 9-pS inward current channel also was observed and its activity also was increased significantly by 8-Br-cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Single L-Type Calcium Channels in Smooth Muscle Cells From Resistance Arteries of Spontaneously Hypertensive Rats

“…The appearance of long-lasting openings in the present study was less frequent than that in bovine pial arteries 14 but was almost the same as that in guinea pig basilar arteries. 18 The reason for the discrepancy among studies is unknown, but it might be due to the difference in tissues or to the recording conditions, such as stimulus frequency, holding potential level, and temperature.…”

“…First, the regulation of channel activity might be altered. It has been reported that the regulation of the activation of L-type Ca 2ϩ channels involves phosphorylation by protein kinase C 19,20 and by cyclic AMP-dependent kinase, 18,21 some ATP-related mechanism, 6 and GTP-binding protein-dependent mechanism. 22,23 Because the activities of protein kinase C 24,25 and GTP-binding protein 26,27 in vascular smooth muscle cells are reported to be altered in SHR, some of these intracellular mechanisms may explain the alteration.…”

Modulation of Ca 2+ Channels by Cyclic Nucleotide Cross Activation of Opposing Protein Kinases in Rabbit Portal Vein

“…Patch-clamp studies in smooth muscle cells have shown that L-type Ca 2ϩ channel activity can be enhanced by either low concentrations of 8-Br cAMP or the catalytic subunit of PKA. [2][3][4] Stimulation of ␤-adrenergic receptors with Iso has also been shown to increase Ca 2ϩ channel currents. 2,3,[5][6][7] On the other hand, 8-Br cGMP or the NO-releasing agents sodium nitroprusside and SNAP have been reported to lead to a decrease of Ca 2ϩ channel activity.…”

Modulation of Ca2+ channel activity by ATP metabolism and internal Mg2+ in guinea‐pig basilar artery smooth muscle cells.

“…The effect appeared independent of cyclic AMPdependent phosphorylation because this had no effect on Ca2+ current in these cells. Ohya & Sperelakis (1989) (Tewari & Simard, 1994). Thus, there is a difference between this observation and our whole-cell recordings in which, even under severe dephosphorylating conditions, Ca2+ channels continued to function.…”