Membrane patches and whole-cell membranes: a comparison of electrical properties in rat clonal pituitary (GH3) cells.

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A comparison has been made between the electrical properties of excised 'outside-out' patches and whole-cell membranes of GH3 cells using the patch-pipette technique. Despite a complicated surface morphology, which includes numerous microvilli, ruffles and blebs, high-resistance seals (typically greater than 10(11) omega) were consistently formed between patch pipettes and GH3 cell membranes. When the internal solution contained 120 mM-CsF, outward currents through K channels were blocked and large Na channel currents were consistently observed in the whole-cell recording mode. Using the same solutions, single Na channel currents were readily observed in outside-out patches. Averaging patch currents yielded macroscopic currents showing the same voltage-dependent kinetics as those observed for the whole-cell membrane. The current vs. voltage and inactivation time constant vs. voltage relationships for the Na channel shifted towards more negative potentials (25 mV or more) within approximately 30 min after going into the whole-cell recording mode. These same relationships could be measured for outside-out patches and their positions along the voltage axis coincided with the asymptotic values measured in the whole-cell mode. When the internal solution contained 120 mM-N-methylglucamine fluoride and the external solution contained 120 mM-Tris chloride, no ionic channel currents could be observed either for whole-cell or outside-out patch membranes. Under these conditions, displacement currents induced by tetraphenyl borate (TPB) were recorded in both types of membranes. The total charge moved showed a sigmoidal dependence upon the applied voltage for both whole-cell and outside-out patch membranes. The charge vs. voltage relationship showed a shift along the voltage axis similar to that observed for Na channels except that the magnitude of the shift was larger. A shift in this relationship was also observed for excised patches but the observable magnitude of the shift was smaller than that in the whole-cell recording mode. The asymptotic values of the charge vs. voltage relationship were similar for whole-cell and outside-out patches, as were the asymptotic values for the translocation time constants. It is concluded that there are no fundamental differences in the properties of ionic channel and displacement currents between whole-cell membranes and excised membrane patches.(ABSTRACT TRUNCATED AT 400 WORDS)

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