Resumen
Single-channel Ba++ current recordings have been made from the insulin-secreting cell line RINm5F with the patch-clamp technique. We have found two different single-channel currents. Both were distinguished kinetically by applying depolarizing test pulses at various levels from different holding potentials (Hp). Jumps from -70 to -30 mV were insufficient to trigger channel openings, but larger depolarizations evoked L-type unitary inward current. Depolarizing voltage pulses from -90 to -30 or -20 mV activate a different Ca++ -channel current characterized by a smaller conductance. This T-type channel activity is not seen with large depolarizing voltage pulses. Glvceraldehyde, a substance evoking insulin secretion from the RINm5F cells, enhance the voltage-activated L-type Ca++ channel opening by increasing the mean open-time and also decreases the voltage threshold for channel opening. Stimulation of the cells with the membrane permeable diacilglycerol analogue didecanoylglvcerol (DC-10, 5 Ug/ml) markedly enhance the open-time of channels during depolarizing voltage pulses. It seems possible that carbohydrate-evoked cellular Ca++ uptake is mediated via protein-kinase C activation.
