Stimulation of urinary acidification by insulin in the turtle bladder

Addition of insulin to the substrate-containing serosal solution of freshly excised bladders or to that of bladders incubated overnight in substrate-enriched media increases the rate of H+ secretion to a greater extent in the latter (overnight group) than in the former. This effect can be blocked by pretreatment with anti-insulin antibody, suggesting that the stimulation of H+ secretion is a specific effect of insulin. The effect of insulin is concentration dependent with half-maximal stimulation of H+ secretion at 100 mU/ml and maximal stimulation at 250 mU/ml. Other characteristics of the insulin-induced stimulation of H+ secretion were its independence of any effect of Na transport and its absolute requirement for the presence of substrate (glucose or pyruvate) under aerobic conditions only. The proton-secreting action of insulin is associated with an increase in the proton-selective conductance in series with the proton pump while the estimated electromotive force of the proton pump remains constant. Finally, the insulin-induced and aldosterone-induced stimulations of proton secretion are mutually independent, as shown by the additivity of these events and by the fact that the effect of insulin was not blocked by pretreatment with cycloheximide. These data suggest that endogenous insulin modulates the rate of H+ secretion by the in vivo turtle bladder.