Triggering of lymphocyte capping appears not to require changes in potential or ion fluxes across the plasma membrane.

Capping induced by anti-Ig antibody on mouse spleen lymphocytes was found to proceed normally over a wide range of membrane potentials from approx. 0 to -65 mV, as estimated with fluorescent probes. The potential was manipulated by ionic substitution in the medium and/or application of gramicidin. Various agents which inhibit capping had differing effects on the membrane potential, some producing no measurable change, others depolarising the cells. In particular valinomycin (10-7 M) was found to inhibit capping in cells both slightly hyperpolarised from the normal resting potential, and fully depolarised. Valinomycin was found to deplete the lymphocytes markedly of ATP and this effect was sufficient to account for the inhibition of capping. Capping occurred in a simplified (sucrose) medium lacking Na+, K+ and Ca2+, suggesting that fluxes across the plasma membrane of these ions are not required. It is concluded that after ligand binding, some reorganisation of receptor protein at the inner face of the membrane is the sufficient stimulus for the intracellular rearrangements involved in capping.