Ionic control mechanisms of mouse pancreatic beta-cell action potentials ("spikes"), in response to glucose, were studied by measuring membrane potentials with intracellular microelectrodes. The curve relating the peaks of the spikes to the log of the external calcium concentration above 10 mM has a slope of 25 mV/10-fold increase of Ca2+. This approaches the value predicted by the Nernst equation for a pure Ca2+ electrode. Increasing the external [Ca2+]o from 0 to 42.5 mM caused an increase in rates of spike depolarization and repolarization. Lowering [Ca2+]o or applying Ca2+ conductance blockers, including Co2+ (1.25 mM), Mn2+ (2mM), and D-600 (2 X 10(-4) M), caused a decrease in rates of spikes depolarization and repolarization, with an increase of [Ca2+]o reversing this effect. Higher concentrations of these Ca2+-conductance blockers eliminated the spike activity. Quinidine at a high concentration (10(-3) M) blocked spike repolarization. Tetraethylammonium (TEA, 25 mM) increased spike amplitude and duration. Therefore, it is concluded that Ca2+ entry during the spike affects potassium permeability, which is inhibited by TEA. Also, there is a competitive binding between Co2+, Mn2+, Mg2+, and Ca2+, the charge carrier. These cations may have an additional action of substituting for Ca2+ to "stabilize" the membrane.

There were 340 episodes of severe diabetic ketoacidosis in 257 patients, July 1, 1965 to June 30, 1968. Fatality in thirty-two cases was associated with significantly elevated admission serum glucose, urea nitrogen, osmolality and age. Major associated causes of death were infection and myocardial infarction. Twenty episodes of acute pancreatitis, with only two deaths, demonstrated severe morbidity and marked elevation of serumglucose and urea nitrogen. Fourteen of the twenty occurred in alcoholics. There were eleven episodes in ten pregnant women, with one maternal and seven fetal deaths. Admission serum potassium, recorded in 336 episodes, was markedly elevated in 22 per cent and decreased in 4 per cent. Including all multiple admissions, there were 482 episodes; forty had hypoglycemic reactions, none with fatality or severe morbidity. Nine cases of nonketotic hyperosmolar coma, with five deaths, demonstrated very high admission serum glucose, urea nitrogen, and osmolality levels.

Pulses of hyperpolarizing current were injected through the microelectrode recording the electrical activity of beta-cells in order to measure input resistance. Increase in resistance during depolarization of the slow oscillation ("burst") indicates inactivation of an outward current, probably K+. Decrease in resistance as the plateau commences suggests that the previous depolarization causes activation of an inward current, probably calcium. The postburst hyperpolarization, caused by a late activation of potassium permeability (PK), would result from the increase of intracellular free calcium. An intracellular buffering system may control this intracellular free calcium level. By restoring the silent phases, in the presence of ouabain or high potassium, injection of hyperpolarizing current shows also a voltage dependency of the PK involved in the postburst hyperpolarization. Glucose, by stimulating intracellular binding of calcium, would cause membrane depolarization at glucose levels below threshold and elongation of the plateau phase at higher concentrations.

The influence of forskolin and 3-iso-butyl-1-methylxanthine (IBMX) on mouse pancreatic beta-cell electrical activity, whole islet cAMP content, and insulin release were investigated. The two drugs potentiated to a similar extent both glucose-stimulated electrical activity and insulin release. In terms of the electrical response, both drugs potentiated the silent depolarization of the membrane in response to low (substimulatory) glucose concentrations, whereas at higher (stimulatory) glucose concentrations they caused an increase in the plateau fraction, with a response similar to the effect of increasing the glucose concentration. Both phases of insulin release were increased by each of the drugs. Ten micromolar forskolin and 100 microM IBMX caused an increase in intraislet adenosine 3',5'-cyclic monophosphate (cAMP) in the presence of 11.1 mM glucose, the former a 17-fold and the latter a 2-fold increase over the cAMP concentration in the presence of glucose alone. Because the two drugs lead to an increase in islet cAMP content, it is proposed that protein phosphorylation resulting from an activation of beta-cell cAMP-dependent protein kinases is responsible for the potentiation of the glucose-induced insulin release and beta-cell electrical activity. The observed effects on electrical activity are compatible with the hypothesis that cAMP-dependent phosphorylation induces alteration of the kinetics of the calcium-sensitive potassium permeability of the beta-cell plasma membrane. The increase in calcium entry into the beta-cell that would result from these alterations may be responsible for the cAMP-dependent potentiation of insulin release.

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