Protein kinase‐C mediates dual modulation of L‐type Ca²⁺ channels in human vascular smooth muscle

Abstract

The role of protein kinase C @'KC) in cellular regulation of L-type Car' channels was investigated in human umbilical vein smooth muscle. Activation of PKC, by low concentrations (< 30 nM) of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) caused inhibition of Ca*' channels, while higher concentrations of TPA (>lOO nM) elicited a transient rise, followed by sustained inhibition of Ca*' channel activity in cell-attached patches. Low TPA concentrations predominantly reduced channel availability, while high concentrations of TPA (100 nM) transiently increased channel availability and, in addition, prolonged mean open time. The inactive 4-a-phorbol-12,13didecanoate failed to affect channel activity, and pretreatment of the cells with PKC inhibitors (H-7, chelerythrine) antagonized inhibitory and stimulatory effects of TPA. Our results provide evidence for two distinct PKC-dependent mechanisms of L-type Ca*' channel regulation in smooth muscle.

Basal dephosphorylation controls slow gating of L‐type Ca2+ channels in human vascular smooth muscle

“…Tautomycin markedly inhibited mean Ca 2÷ channel activity in human vascular smooth muscle. This finding is in accordance with the concept of smooth muscle L-type Ca 2+ channels being subject to phosphorylation-dependent down-regulation [4][5][6][7]. Inhibitory phoshorylation of smooth muscle Ca 2+ channels has been suggested to involve cyclic nucleotide-dependent protein kinases [6] and/or specific isoforms of protein kinase C [7].…”

“…the channels' availability. We have recently reported on a dual regulation of human smooth muscle Ca 2+ channels by activation of protein kinase C [7], and demonstrated that protein kinase C-mediated inhibition is associated with reduced channel availability. Similarly the inhibitory effect of tautomycin was found to be based predominantly on a reduction of channel availability.…”

“…Recent evidence suggests phosphorylation-dependent control of specific kinetic functions of cardiac L-type channels [2,3]. Modulatory phosphorylation of smooth muscle L-type channels differs strikingly from those of cardiac and skeletal muscle L-type channels, in that phosphorylation appears to mediate not only stimulation but also inhibition of Ca 2+ channels in smooth muscle [4][5][6][7]. Phosphorylation-dependent inhibition of smooth muscle L-type Ca 2÷ channels has been demonstrated in studies with protein kinase activators [6,7] as well as protein phosphatase inhibitors [4,5].…”

“…Modulatory phosphorylation of smooth muscle L-type channels differs strikingly from those of cardiac and skeletal muscle L-type channels, in that phosphorylation appears to mediate not only stimulation but also inhibition of Ca 2+ channels in smooth muscle [4][5][6][7]. Phosphorylation-dependent inhibition of smooth muscle L-type Ca 2÷ channels has been demonstrated in studies with protein kinase activators [6,7] as well as protein phosphatase inhibitors [4,5]. Inhibitory modulation of smooth muscle Ca 2+ channels may be based on (i) a reduction of channel availability, (ii) a reduction of open probability of available channels or (iii) suppression of both availability and open probability.…”

Desensitization of the μ‐opioid activation of phospholipase C in SH‐SY5Y cells: the role of protein kinases C and A and Ca2+‐activated K+ currents

“…Indeed, PKC has been reported to uncouple G-proteins from opioid receptors in guinea-pig striatal membranes and SH-SY5Y cells (Lin et al, 1994). Furthermore, PKC is known to modulate the activity of various ion channels (Shearman et al, 1989;Petersen & Berridge, 1994;Tuominen et al, 1994), including the L-type VSCC (Schuhmann & Groschner, 1994). As activation of PLC stimulates PKC activity, via diacylglycerol, in addition to stimulating Ins(1,4,5)P3 formation (Berridge, 1993), p-opioids would also be expected to increase PKC activity in SH-SY5Y cells.…”