Similarity of unitary Ca2+ currents in three different species.

Membrane Ca2+ currents are the triggers for numerous cellular activities such as secretions, contraction, and oscillations in neural discharge. Different Ca2+ channels are assumed to subserve the various functions; this does not apply to Na+ currents for which there is thought to be only one type of channel. We have examined single Ca2+ channels in cells from three very different species (bird, snail and rat) using the patch-clamp method, and report here that unitary events consisted of small, brief current pulses that often occurred in bursts and were similar for all three species. Thus, reported differences among various Ca2+ current must have other origins.