Catecholamine stimulation of ion transport in the toad urinary bladder

Autonomic control of the urogenital tract

The urogenital tract houses many of the organs that play a major role in homeostasis, in particular those that control water and salt balance, and reproductive function. This review focuses on the anatomical and functional innervation of the kidneys, urinary ducts and bladders of the urinary system, and the gonads, gonadal ducts, and intromittent organs of the reproductive tract. The literature, especially in recent years, is overwhelmingly skewed toward the situation in mammals. Nevertheless, where specific neurochemical markers have been investigated, common patterns of innervation can be found in representatives from most vertebrate classes. Not surprisingly the vasculature, epithelia and smooth muscle of all urogenital organs receives adrenergic innervation. These nerves may contain non-adrenergic non-cholinergic (NANC) neurotransmitters such as ATP and NPY. Cholinergic nerves increase motility in most urogenital organs with the exception of the kidney. The major NANC nerves found to influence urogenital organs include those containing VIP/PACAP, galanin and neuronal nitric oxide synthase. These can be found associated with both smooth muscle and epithelia. The role these nerves play, and the circumstances where they are activated are for the most part unknown.

Norepinephrine stimulation of sodium transport in Necturus urinary bladder

Norepinephrine alters the transepithelial electrical properties of an open-circuited urinary bladder from the mud puppy, Necturus maculosus. When 10(-5) M norepinephrine is superfused over the serosa of the epithelium, the transepithelial voltage (Vt) and short-circuit current (Isc) increase as the resistance (Rt) decreases. The norepinephrine-mediated changes are reversed by the addition of amiloride (5.10(-5) M) to the mucosal Ringer's solution. The serosal adrenoceptors mediating the Na+ transport are more sensitive to norepinephrine (EC50 = 1.2.10(-6) M) than to epinephrine or isoproterenol. Since the Isc is blocked selectively by the antagonist, phenoxybenzamine, stimulation of active transepithelial Na(+)-flux by catecholamines is mediated by an alpha-adrenoceptor. The apical cell membrane voltage (Va) and fractional resistance (fRa) were recorded using conventional KCl-filled microelectrodes. Untreated tissues have Va close to 0 mV while the basolateral membrane voltage (Vb) is between -85 and -95 mV. About 90% of Rt is apical cell membrane resistance (fRa). When amiloride inhibits sodium transport, Va becomes negative, Vb hyperpolarizes slightly and fRa increases to 97%. On the other hand, if the bladders are treated with norepinephrine, fRa decreases to 79% as Va becomes positive and Vb depolarizes. When Rt changes, the resistance of the paracellular pathway (Rp) is unaltered. Changes in the electrical properties of the tissue appear to be mediated primarily by alterations in Ra. Since the Necturus bladder does not respond to antidiuretic hormone, this study implies that biogenic amines regulate Na+ transport in the epithelium.