Role of intracellular calcium in renal proximal tubule cell volume regulation.
Osmoregulatory Ca2+ signaling in hypotonic solutions was studied with videometric techniques in 158 proximal renal tubules isolated from the teleost Carassius auratus. Absence of extracellular Ca2+, hypoxia (23 mmHg), or NaCN (3 mM) did not alter regulatory volume decreases (RVD). Nevertheless, decrements of intracellular Ca2+ via the A23187 ionophore or after intracellular Ca2+ chelation with indo-1/AM (5 microM) inhibited RVD. In tubules depleted of Ca2+, RVD could only be fully elicited when intracellular Ca2+ pulses were given within 1 min after hypotonic stimulation. While inhibition of Ca2+ release from the endoplasmic reticulum (ER) with 8-(diethylamino)octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8, 50 microM) blunted RVD, some of its effects could be reversed with the anion carrier tributyltin (1 microM). Dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP, 0.5 and 1.0 mM) and forskolin (0.25 mM) also impeded RVD; however, their effects could be partially reversed with the K+ ionophore gramicidin (0.5 microM). In conclusion, in Carassius auratus proximal renal tubule cells, RVD is activated by an intracellular Ca2+ signal that likely emanates from the ER and not from the extracellular media or the mitochondrial Ca2+ pool. Ca2+ activation of a cAMP-modulated osmoregulatory K+ channel appears to play an important role.
Terreros
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DA
Veterans Affairs Medical Center, Salt Lake City, Utah.
Kanli
H
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D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006054:Goldfish; D007038:Hypotonic Solutions / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D014882:Water-Electrolyte Balance
D002121:Calcium Channel Blockers; D007038:Hypotonic Solutions; C006014:8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate; D005707:Gallic Acid; D003994:Bucladesine; D002118:Calcium