Two types of Ca channel in rat pancreatic beta-cells.

Ba currents flowing through single Ca-channels were recorded from cell-attached patches on rat pancreatic beta-cells. Two types of voltage-activated Ca-channels were found. The first (T-type) had a single channel conductance of 8 pS in 100 mM Ba, was activated at a low threshold (around -50mV) and inactivated by holding potentials positive to -40 mV. These properties are similar to those described for T-type channels in other preparations. The second type of Ca-channel (L-type) had a single channel conductance of 20pS in 100 mM Ba, was activated at a higher threshold (greater than -30mV), showed little inactivation during a 250 ms pulse and could be activated from a holding potential of -40mV. The dihydropyridine agonist BAY K 8644 selectively prolonged L-type Ca-channel openings. These properties are characteristic of L-type Ca-channels.