Intracellular pH regulation in isolated trout gill mitochondrion-rich (MR) cell subtypes: Evidence for Na +/H + activity

Abstract

We have studied intracellular pH (pH i) recovery in isolated trout gill mitochondrion-rich (MR) cells following acidification by the NH 4Cl pre-pulse technique. Within a mixed MR cell population, one cell type displayed Na +-independent pH i recovery while the other cell type lacked a Na +-independent pH i recovery. Cells displaying Na + independent recovery exhibited a significantly higher buffering capacity compared to cells lacking Na +-independent pH i recovery. Cells displaying Na + independent recovery were identified as PNA + (peanut lectin agluttinin binding) MR cells while those unable to recover were identified as PNA − (non-peanut lectin agluttinin binding) MR cells. Therefore, recovery from acidification in the absence of Na + provides a direct functional marker for PNA + and PNA − MR cells. Re-addition of Na + to acidified cells resulted in a transient pH i recovery in both cell types. This event was abolished by amiloride (500 µM) but it was insensitive to phenamil (50 µM). The phorbol ester PMA (1 µM) potentiated the Na + induced pH i recovery suggesting that activation by PKC is required for continuous Na +/H + exchanger activity in trout gill MR cells. This study is the first functional description of pH i recovery in lectin-identified trout gill MR cells and provides insight into a putative cellular signaling mechanism that may control pH i regulation in the gill epithelium.