Phorbol myristate acetate inhibits acidification by turtle urinary bladder

Area of Science:

• Physiology
• Cell Biology
• Biochemistry

Background:

• The turtle urinary bladder is a model system for studying distal acidification.
• Protein phosphorylation plays a role in regulating ion transport.
• Phorbol myristate acetate (PMA) activates protein kinase C.

Purpose of the Study:

• To investigate the effects of PMA on acid secretion in the turtle urinary bladder.
• To determine the role of protein phosphorylation in modulating distal acidification.
• To elucidate the mechanism of PMA-induced inhibition of acid secretion.

Main Methods:

• Measurement of reverse short-circuit current (RSCC) and titrimetric acid secretion.
• Dose-response studies with PMA.
• Selective inhibition of proton secretion using adverse pH gradients or 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid.
• Measurement of carbonic anhydrase (CA) cell cytoplasmic pH and cell morphology.
• Assessment of the effects of sodium azide and acetazolamide.

Main Results:

• PMA significantly inhibited RSCC and titrimetric acid secretion in a dose-dependent manner.
• PMA's inhibitory effect was observed only when proton secretion was active.
• PMA reduced CA cell cytoplasmic pH and altered cell morphology.
• The PMA inhibition was azide-insensitive and distinct from acetazolamide.
• PMA's effects were mimicked by 1-oleoyl-2-acetyl-rac-glycerol but not an inactive phorbol ester.

Conclusions:

• PMA decreases basal acid secretion and blocks CO2-stimulated acid secretion via an azide-insensitive pathway.
• Protein kinase C-mediated protein phosphorylation is crucial for regulating the transition between acid and base secretion in the turtle bladder.
• These findings highlight a novel mechanism for controlling distal acidification.