Calcium entry into smooth muscle cells is essential to maintain contractility. In canine jejunal circular smooth muscle cells the predominant calcium entry pathway is through L-type calcium channels. The aim of this study was to determine the G-protein regulation of L-type calcium channel current (I(CaL)) in isolated canine jejunal circular smooth muscle cells. Barium (80 mM) was used as the charge carrier. GTP-γS and GTP increased maximal inward current from 118.7 ± 12 pA to 227.5 ± 21.5 pA (n = 8) and 174.6 ± 10.1 pA (n = 6) respectively. The increase in inward current was blocked bat nifedipine suggesting it was through L-type calcium channels. Pertussis toxin did not alter baseline I(CaL) while cholera toxin increased I(CaL) from 125 ± 19 pA in controls (n = 6) to 347 ± 30 pA (n = 4). Staurosporine inhibited the increase in current evoked by GTP-γS and calyculin further increased I,, over the increase evoked by GTP-γS. The results suggest that cholera toxin sensitive G-proteins activate L-type calcium channels in isolated canine jejunal circular smooth muscle cells through protein phosphorylation.
- Gastrointestinal smooth muscle
- L-type calciun channels
- Patch clamp
ASJC Scopus subject areas
- Cell Biology