Swelling-induced changes in cytosolic [Ca2++] in insulin-secreting cells: a role in regulatory volume decrease?
Exposure of insulin-secreting cells to hypotonic solutions causes cell swelling followed by regulatory volume decrease (RVD). We have previously demonstrated that RVD is due to activation of a Cl(-) conductance. The present study investigates whether changes in cytosolic [Ca(2+)] play a role in these responses. Hypotonic swelling of RINm5F insulinoma cells caused a marked increase in cytosolic [Ca(2+)]. This effect was abolished by omission of extracellular Ca(2+), by the Ca(2+) channel blockers D600 or Gd(3+)and by 4,4'-dithiocyanatostilbene-2,2'-disulphonic acid (DIDS), an inhibitor of the volume-sensitive anion. RVD was markedly impaired in the absence of extracellular Ca(2+), but not by D600 nor by Gd(3+). RVD was also inhibited by the maxi-K(+) (BK(Ca)) channel blockers tetraethylammonium (TEA) and iberiotoxin (IbTx), whereas the K(ATP) channel blocker tolbutamide was ineffective. Cell swelling was accompanied by activation of a K(+) conductance which was sensitive to TEA and IbTx but not to tolbutamide. It is concluded that cell swelling causes activation of the volume-sensitive anion channel, leading to depolarization and Ca(2+) entry via voltage-gated Ca(2+) channels. RVD is a Ca(2+)-dependent process, requiring low 'resting' levels of intracellular [Ca(2+)]. However, the swelling-induced increase in cytosolic [Ca(2+)] is not required for RVD to occur. RVD depends upon simultaneous activation of Cl(-) and K(+) channels. We suggest that the BK(Ca) channel is the major K(+) conductance involved in RVD.
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Department of Medicine, University of Manchester, M13 9WL, Manchester, UK.
Brown
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D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D004553:Electric Conductivity; D007038:Hypotonic Solutions / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007340:Insulinoma / Q000378:metabolism*; D009994:Osmolar Concentration; D010455:Peptides / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism; D051381:Rats; D019789:Tetraethylammonium / Q000494:pharmacology; D014044:Tolbutamide / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D002121:Calcium Channel Blockers; D007038:Hypotonic Solutions; D007328:Insulin; D010455:Peptides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D019789:Tetraethylammonium; C064719:iberiotoxin; D014044:Tolbutamide; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D011188:Potassium; D002118:Calcium