Cytosolic free calcium spiking affected by intracellular pH change.
The characteristics underlying cytosolic free calcium oscillation were evaluated by superfused dual wave-length microspectrofluorometry of fura-2-loaded single acinar cells from rat pancreas. Application of a physiological concentration of cholecystokinin octapeptide (CCK) (20 pM) induced a small basal increase in cytosolic free calcium concentration ([Ca2+]i) averaging 34 nM above the prestimulation level (69 nM) with superimposed repetitive Ca2+ spike oscillation. The oscillation amplitude averaged 121 nM above the basal increase in [Ca2+]i and occurred at a frequency of one pulse every 49 s. Although extracellular Ca2+ was required for maintenance of high frequency and amplitude of the spikes with increase in basal [Ca2+]i, the primary source utilized for oscillation was intracellular. The threshold of the peak [Ca2+]i amplitude for causing synchronized and same-sized oscillations was less than 300 nM. The [Ca2+]i oscillation was sensitive to intracellular pH (pHi) change. This is shown by the fact that the large pHi shift toward acidification (delta pHi decrease, 0.95) led to a basal increase in [Ca2+]i to the spike peak level with inhibiting Ca2+ oscillation. The pHi shift toward alkalinization (delta pHi increase, 0.33) led to a basal decrease in [Ca2+]i to the prestimulation level, possibly due to reuptake of Ca2+ into the Ca2+ stores, with inhibiting Ca2+ oscillation. Whereas extracellular pH (pHo) change had only minimal effects on Ca2+ oscillation (and/or Ca2+ release from intracellular stores), the extra-Ca2+ entry process, which was induced by higher concentrations of CCK, was totally inhibited by decreasing pHo from 7.4 to 6.5. Thus the major regulatory sites by which H+ affects Ca2+ oscillation are accessible from the intracellular space.
Tsunoda
Y
Y
Department of Physiology, University of Michigan, Ann Arbor 48109.
D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008297:Male; D010179:Pancreas / Q000166:cytology / Q000378:metabolism*; D011422:Propionates / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012844:Sincalide / Q000494:pharmacology
D011422:Propionates; D000643:Ammonium Chloride; D012844:Sincalide; D002118:Calcium