[Single calcium channels of spinal ganglion neurons in the rat]

Single calcium channels in isolated dorsal root ganglion cells of the newborn rat were studied using the method of patch clamp in its cell-attached configuration. With 60 mmol/l of Ca2+ in the pipette (extracellular) solution, the amplitude of unitary Ca currents varied from 0.58 +/- 0.05 pA to 0.43 +/- 0.05 pA with a 20 mV change of the potential, which corresponds to a channel conductance of 7 +/- 0.5 pS. The distribution of the open time was monoexponential with the time constant of 0.75 ms not depending on the membrane potential. The distribution of closed time approached a biexponential time course. The fast component (approximately 0.8 ms) showed no dependence on the membrane potential, while the time constant of the slow one decreased with increasing depolarization (from 22 ms to 4 ms with a 20 mV change of the potential). Using experimentally obtained time parameters which describe single calcium channel function and assuming a three-state model of the channel, the numerical values of the rate constants of transitions between individual states were determined.