Different modulation of hepatocellular Na+/H+ exchange activity by insulin and EGF.
Indirect evidence suggests that insulin, like epidermal growth factor (EGF), stimulates liver cell Na+/H+ exchange. We directly studied the effect of insulin on intracellular pH (pHi) and the Na+/H+ exchanger in isolated rat hepatocytes with the fluorescent probe, 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). The effects of insulin were compared with those of EGF. Studies were carried out in the absence of HCO3- and in the presence of acetazolamide to isolate the Na+/H+ exchanger from other pH regulatory mechanisms. Insulin (9 nM) caused a reversible acidification of baseline pHi, whereas no significant effect was observed with EGF (30 nM). pHi was acidified by two different methods (NH4Cl pulse and external Na+ removal) to assess liver cell Na+/H+ exchange activity. In the NH4Cl pulse experiments, insulin had no significant effect on the Na+/H+ exchanger compared with the control (0.141 +/- 0.009 pH units/min, n = 14, and 0.122 +/- 0.023 pH units/min, n = 16, respectively). However, in the same conditions, EGF nearly doubled the rate of the Na+/H+ exchange activity (0.193 +/- 0.015 pH units/min, P < 0.05, n = 6). In the Na+ removal experiments, EGF again significantly increased the pHi recovery rate (0.542 +/- 0.032 pH units/min, n = 3) compared with the control (0.227 +/- 0.028 pH units/min, n = 5) and insulin (0.245 +/- 0.053 pH units/min, n = 5). Compared with control conditions, a subchronic administration of insulin (9 nM) in vitro had no significant effect on the Na+/H+ exchanger, nor did it affect baseline pHi.(ABSTRACT TRUNCATED AT 250 WORDS)
Haimovici
J
J
Department of Pharmacology, Université de Montréal, Québec, Canada.
Beck
J S
JS
Molla-Hosseini
C
C
Vallerand
D
D
Haddad
P
P
D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D002021:Buffers; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers; D012996:Solutions; D013997:Time Factors
D002021:Buffers; D007328:Insulin; D017923:Sodium-Hydrogen Exchangers; D012996:Solutions; D000643:Ammonium Chloride; D004815:Epidermal Growth Factor; D012964:Sodium