Membrane conductance oscillations induced by serum in quiescent human skin fibroblasts.

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Abstract
1. Application of fetal calf serum to quiescent human fibroblasts, kept under whole‐cell voltage clamp at positive potentials, induced a series of transient rises in membrane conductance. 2. The first transient increase in conductance developed with very short time lag (2‐10 s) after serum addition, while the period between successive transients was 30‐90 s, being remarkably constant in each particular cell. 3. Raising the Ca2(+)‐buffering capacity of the intracellular solution with 1 mM‐EGTA suppressed the appearance of the sustained oscillations. 4. The conductance increase was strongly voltage dependent: voltage ramps applied before, during and after the transients revealed the activation of an outwardly rectifying conductance with variable reversal potentials (between +14 and ‐55 mV). 5. No significant shifts of the reversal potential were observed when the extracellular K+ concentration was increased to 126 mM. Substitution of K+ with Cs+ as intracellular cation eliminated the outward current in response to serum. 6. External application of the Ca2+ ionophore A23187 elicited currents which were very similar in voltage dependence and time course to those triggered by serum. 7. The serum‐induced response persisted unaffected by the absence of external Ca2+. The response was also seen in the presence of 1 mM‐Cd2+ in the external solution. 8. Serum addition caused a rapid morphological rearrangement of the cells. 9. It is concluded that serum triggers a mobilization of Ca2+ from intracellular stores which in turn activates cationic channels.

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