ABSTRACT
Mitochondrion-rich (MR) cells are present in large numbers in the gill and opercular epithelia of estuarine teleosts. This chapter examines the mechanism of ion transport by mitochondrion-rich MR cells and its rapid regulation in teleost fish. Small estuarine fish experience rapid shifts in salinity in intertidal microenvironments. Elucidation of the regulatory pathways terminating at channels and transporters will be important to understanding ion transport regulation in health and disease. The chapter reviews the hormonal control of osmoregulation in fish. Typically, the cells appear with a smaller accessory cell entwined with the larger cell and between the accessory cells and MR cells is a leaky paracellular pathway that allows transepithelial transport of sodium down its electrochemical gradient. Many factors are known to affect chloride secretion in teleost fish pharmacologically, including hormones and neurotransmitters that inhibit secretion: catecholamines, via α-2 adrenoceptors, acetylcholine via muscarinic receptors, somatostatin and urotensin II.
