Regulation of renal Na-HCO3 cotransporter: VIII. Mechanism Of stimulatory effect of respiratory acidosis.
We examined the effect of respiratory acidosis on the Na-HCO3 cotransporter activity in primary cultures of the proximal tubule of the rabbit exposed to 10% CO2 for 5 min, 2, 4, 24 and 48 hr. Cells exposed to 10% CO2 showed a significant increase in Na-HCO3 cotransporter activity (expressed as % of control levels, 5 min: 142 +/- 6, 2 hr: 144 +/- 13, 4 hr: 145 +/- 11, 24 hr: 150 +/- 15, 48 hr: 162 +/- 24). The increase in activity was reversible after 48 hr. The role of protein kinase C (PKC) on the stimulatory effect of respiratory acidosis on the cotransporter was examined in presence of PKC inhibitor calphostin C or in presence of PKC depletion. Both calphostin C and PKC depletion prevented the effect of 10% CO2 for 5 min or 4 hr to increase the activity of the cotransporter. 10% CO2 for 5 min or 4 hr increased total and particulate fraction PKC activity. To examine the role of phosphotyrosine kinase (PTK) on the increase in cotransporter activity we studied the effect of two different inhibitors, 2-hydroxy-5-(2,5-dihydroxylbenzyl) aminobenzoic acid (HAC) and methyl 2,5-dihydroxycinnamate (DHC) which inhibit phosphotyrosine kinase in basolateral membranes. Cells were pretreated either with vehicle or HAC or DHC and then exposed to 10% CO2 for 5 min or 4 hr. In cells treated with vehicle, 10% CO2 significantly increased cotransporter activity as compared to control cells exposed to 5% CO2. This stimulation by 10% CO2 was completely prevented by HAC or DHC at 5 min (5% CO2: 1.8 +/- 0.2, 10% CO2: 2.6 +/- 0.2, 10% CO2 + HAC: 1.6 +/- 0.2, 10% CO2: +DHC: 2.0 +/- 0.3 pH unit/min) and also at 4 hr. The protein synthesis inhibitors actinomycin D and cycloheximide appear to prevent the effect of 10% CO2 for 4 hr on the cotransporter. Our results show that early respiratory acidosis stimulates the Na-HCO3 cotransporter through PKC and PTK-dependent mechanisms and the late effect appears to be mediated through protein synthesis.
Ruiz
O S
OS
Section of Nephrology, University of Illinois at Chicago and West Side VA Medical Center, IL 60612-7315, USA.
Qiu
Y Y
YY
Wang
L J
LJ
Cardoso
L R
LR
Arruda
J A
JA
D000142:Acidosis, Respiratory / Q000378:metabolism*; D000222:Adaptation, Physiological; D062365:Aminobenzoates / Q000494:pharmacology; D000818:Animals; D002245:Carbon Dioxide; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D002934:Cinnamates / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D011493:Protein Kinase C / Q000502:physiology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011817:Rabbits; D012459:Salicylates; D027982:Sodium-Bicarbonate Symporters; D062368:meta-Aminobenzoates
D062365:Aminobenzoates; D002352:Carrier Proteins; D002934:Cinnamates; D004791:Enzyme Inhibitors; D011500:Protein Synthesis Inhibitors; D012459:Salicylates; D027982:Sodium-Bicarbonate Symporters; D062368:meta-Aminobenzoates; C073254:2-hydroxy-5-(2,5-dihydrobenzyl)aminobenzoic acid; D002245:Carbon Dioxide; D003609:Dactinomycin; C067472:methyl 2,5-dihydroxycinnamate; D003513:Cycloheximide; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C