The maintenance of resting potentials in glycerol-treated muscle fibres.

1. A modification of a previously published method for the disruption of the T-tubules of frog skeletal muscle is described. The modification permits the disruption of the T-tubules without the decline in resting potentials which was reported previously.2. The method for the disruption of the T-tubules involves the washout of glycerol following loading in a 400 mM glycerol Ringer solution. The modification consists of elevating the concentration of divalent cations in the Ringer used for glycerol washout.3. The optimum concentrations are 5 mM-Ca(2+) and 5 mM-Mg(2+) added as their chloride salts. Neither 10 mM-Ca(2+) nor 10 mM-Mg(2+) are as effective as the combination of each at 5 mM. Other concentrations gave less satisfactory results.4. The use of the modified technique provides a preparation which maintains 85-90 mV resting potentials for up to 6 or 8 hr but which will not contract in response to membrane depolarization.