Patch and whole cell calcium currents recorded simultaneously in snail neurons.

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Abstract
The flow of Ca ions through single Ca channels was examined in Helix pomatia. The gigaseal method was used on identifiable neurons that were voltage clamped using a 2-microelectrode voltage clamp method. Average Ca patch currents and whole cell currents have similar time courses. They are affected similarly by changes in temperature. The differences in amplitude and inactivation between Ba and Ca whole cell currents were present in the patch records. The stationary noise spectra recorded from ensembles of multichannel patches have 2 components with fast and slow time constants equivalent to 2 components in the whole cell tail current relaxations. Elementary current amplitudes measured from the variance-mean relationship and from noise spectra gave values comparable to measurements from single channels. The single channel I-V relationship was curvilinear and the maximum slope conductance in 40 mM Cao was 7 pS [pica Siemen]. The amplitude of unitary currents was unchanged at long times when inactivation had occurred; hence depletion is not involved in this process. Channel density was .apprx. 3 .mu.m-2 and was the same for Ba and Ca currents. The whole cell asymmetry currents gave very large values for the gating charge per channel. Changes in temperature from 29.degree. to 9.degree. C had only a slight effect on the 2 Ca current .tau. [time constant] at potentials where turn-on of patch and whole cell currents was markedly slowed and the peak amplitudes were reduced by 1/3. Single channel recordings were obtained at these 2 temperatures, and the mean open time and the fast component of the closed times were scarcely affected. Unit amplitudes were reduced by 30% and the slow closed time component was doubled. Therefore, peak currents were reduced partly as a result of the reduction in unit amplitude, but mainly as a result of a reduction in opening probability, the latter arising from an increase of the long closed times. The behavior of single Ca channels in membrane patches is the same as it is in the whole cells. Cooling from 29.degree. to 9.degree. C acts primarily on transitions among closed states and has little effect on the open to closed transition.