The electrogenic sodium pump in the hyperpolarizing and secretory effects of pancreozymin in the pancreatic acinar cell.

Abstract

SUMMARY1. Transmembrane potential, effective membrane resistance, and amylase release were recorded simultaneously from acinar cells of isolated rat pancreas perfused with Krebs-Henseleit solution.2. The hyperpolarizing effect of pancreozymin (Pz) was confirmed by perfusing with a solution containing 5 m-u. Pz/ml.3. The hyperpolarizing effect of Pz disappeared in the following environments: (a) in low ambient temperature, (b) in K-free medium, (c) in low Na medium, and (d) in the presence of ouabain. In these environments, transient depolarization was frequently observed immediately after stimulation.It is suggested that there are two components in the effect of Pz on the membrane potential of the acinar cells: transient depolarization which coincides with an increase in Na permeability in the initial phase, and continuous hyperpolarization due to an electrogenic Na pump which conceals transient depolarizing phase when the pump is dominant.4. The secretary effect of Pz was inhibited under conditions that suppressed the electrogenic Na pump.It is proposed that the Na pump activated by Pz maintains the passive Na-influx, increases [Ca2+]I, and, in consequence, upholds the amylase output during continuous stimulation. 5. A medium which was used to bathe the sectioned pancreas with Pz was found to contain a substance which depolarized the acinar cells.

The potentiating influences of insulin on pancreozymin‐induced hyperpolarization and amylase release in the pancreatic acinar cell.

“…The concentration of Pz is expressed in Crick, Harpar & Raper (1950) (Kanno, 1975). One unit of amylase activity in the pancreatic juice or the perfusate was defined as the amount of enzyme which produced 1 mg maltose during a 5 min incubation with the diluted perfusate at 37 TC by the modified method.…”

Physiology of Paraneurons

“…The depolarization induced by ACh, even when large and rapid in onset, was not accompanied by evidence of spike generation. Similar experiments were carried out in recent years on isolated and perfused adrenal medulla of guinea pigs (T. KANNO, E. HARADA and K. ISHIKAWA; quoted by KANNO, 1976). Chromaffin cells were rapidly depolarized by carbamylcholine or by passing current through the recording electrode; but they did not generate action potentials, and appeared to be electrically inexcitable.…”

“…A similar speculation has been made in the pancreatic acinar cell (KANNO, 1972). In fact, JOHNSON and ScARPA (1976) have recently shown that the isolated chromaffin granule is impermeable to the cati.ons tested (Na+, K+, H+, Ca++ and Mg++).…”

“…To correlate the depolarization with the extrusion of catecholamine, intracellular membrane potential and effective membrane resistance had been recorded from several chromaffin cells in the course of perf using the adrenal medulla of the guinea pig and the rat (T. KANNO, E. HARADA and K. ISHIKAWA; quoted by KANNO, 1976). The results showed that both ACh and carbamylcholine depolarized the chromaffin cells, decreased effective membrane resistance, and augmented adrenaline extrusion.…”

“…Activated state of secretion: stimulus-extrusion (secretion) coupling Adrenal chromaffin cell. Among a wide variety of secretory cells including paraneurons, the cellular mechanism of catecholamine extrusion from the adrenal chromaffin cell has been most extensively investigated, and the cell is now regarded as a leading model for secretion (see DOUGLAS, 1968DOUGLAS, , 1975DOUGLAS, , 1976RUBIN, 1970aRUBIN, , 1974KANNO, 1968KANNO, , 1976, and as a typical paraneuron (KOBAYASxi, 1976). To include all the events occurring in the activated state of the secretion, the term "stimulus-secretion coupling" was proposed by DOUGLAS and RUBIN (1961).…”