Efflux of 86Rb from rat and mouse pancreatic islets: the role of membrane depolarization

Br J Pharmacol. 1984 Nov;83(3):831-9. doi: 10.1111/j.1476-5381.1984.tb16239.x.

Abstract

The efflux of 86Rb from rat or mouse perifused islets preloaded with the isotope has been used as an index of the potassium permeability of the islet beta-cell membrane. Cellular transmembrane potentials were altered by changing [K]O or by direct electrical stimulation and the effects on potassium permeability examined. Omission of KCl from the medium perifusing rat islets induced a biphasic change in 86Rb efflux, a brief decline being superseded by a pronounced increase in efflux. Re-introduction of KCl, 4.7 mM, caused a further increase in 86Rb efflux preceding a return to control values. Increasing [K]O from 4.7 mM to 10 mM, 20 mM or 47 mM caused a phasic increase in 86Rb efflux with the magnitude of both the peak and average rate of efflux being dependent upon the extent of the change in [K]O. The increase in 86Rb efflux produced by [K]O, 47 mM, was attenuated by Co2+, 2.56 mM (51% inhibition) or quinine, 10 microM (47% inhibition), but efflux remained significantly (P less than 0.001) above control values. Electrical stimulation of single microdissected mouse pancreatic islets by currents of 0.1 to 0.5 mA evoked a rapid, phasic increase in 86Rb efflux. The magnitude of the response was unaffected by EGTA, 2 mM, or nupercaine, 100 microM. These observations are discussed in relation to the mechanisms controlling the potassium permeability, membrane potential and insulin secretion of the pancreatic islet beta-cell. It is concluded that beta-cell depolarization by a raised [K]0 increases potassium permeability and efflux by at least two mechanisms: (i) a calcium-dependent potassium efflux triggered by an increase in [Ca]i and (ii) an activation of voltage-sensitive potassium channels which occurs even when the calcium-dependent potassium permeability is blocked.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cobalt / pharmacology
  • Electric Stimulation
  • Extracellular Space / metabolism
  • In Vitro Techniques
  • Islets of Langerhans / metabolism*
  • Kinetics
  • Male
  • Mice
  • Perfusion
  • Potassium / metabolism
  • Quinine / pharmacology
  • Radioisotopes / metabolism
  • Rats
  • Rats, Inbred Strains
  • Rubidium / metabolism

Substances

  • Radioisotopes
  • Cobalt
  • Quinine
  • Rubidium
  • Potassium