Dynamics of Ca2+i and pHi in Ehrlich ascites tumor cells after Ca2+-mobilizing agonists or exposure to hypertonic solution.
Intracellular free calcium concentration ([Ca2+]i) and intracellular pH (pHi) were monitored in Ehrlich ascites tumor cells using Fura-2 or 2',7',-bis-(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF), or both probes in combination. An increase in [Ca2+]i induced by thrombin or bradykinin, agonists known to elicit transient cell shrinkage in these cells, evoked a transient intracellular acidification, followed by an alkalinization. The latter was due to activation of a Na+/H+ exchanger and was inhibited under conditions preventing agonist-induced cell shrinkage without preventing the increase in [Ca2+]i. In contrast, a smaller, slower increase in [Ca2+]i elicited by thapsigargin did not cause cell shrinkage, and did not activate the Na+/H+ exchanger. Exposure to hypertonic solution was not associated with an increase in [Ca2+]i, but elicited an intracellular alkalinization similar to that induced by thrombin or bradykinin, via activation of the Na+/H+ exchanger. Thus, activation of the exchanger by the Ca2+-mobilizing agonists is suggested to be secondary to the cell shrinkage induced by these compounds. NH4Cl-induced intracellular alkalinization resulted in an increase in [Ca2+]i, apparently via stimulation of Ca2+ influx, whereas shrinkage-induced intracellular alkalinization did not stimulate Ca2+ influx. Thus, cell shrinkage appears to inhibit the Ca2+ influx otherwise resulting from alkalosis. In agreement with that notion, thapsigargin-induced Ca2+ influx was inhibited by cell shrinkage.
Pedersen
S F
SF
Biochemistry Department, August Krogh Institute, 13, Universitetsparken, 2100 Copenhagen O, Denmark.
Jørgensen
N K
NK
Hoffmann
E K
EK
D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D048429:Cell Size; D005452:Fluoresceins; D005456:Fluorescent Dyes; D016257:Fura-2; D006863:Hydrogen-Ion Concentration; D006982:Hypertonic Solutions; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology; D019284:Thapsigargin / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology*
D005452:Fluoresceins; D005456:Fluorescent Dyes; D006982:Hypertonic Solutions; D017923:Sodium-Hydrogen Exchangers; D000643:Ammonium Chloride; D019284:Thapsigargin; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D013917:Thrombin; D001920:Bradykinin; D002118:Calcium; D016257:Fura-2