Effects of variations in extracellular osmolality on spontaneous contractile activity and response to nerve stimulation in rat detrusor muscle in vitro.
The effects of hyperosmolar (390, 590 mosm/kg) and hypoosmolar (260 mosm/kg) solutions on myogenic spontaneous contractile activity and response to nerve stimulation were studied on strips of rat detrusor muscle in vitro. In isotonic (290 mosm/kg) solution the mean spontaneous contractile activity was 2.1 +/- 0.6% and the amplitude of the largest spontaneous contractions was 9.8 +/- 3.0% of maximal response to nerve stimulation. In 390 mosm/kg the frequency of spontaneous contractions decreased, but due to a fourfold increase of contraction amplitude a threefold increase of mean contractile activity was recorded. In 260 mosm/kg a similar contraction pattern as in 290 mosm/kg was seen. The spontaneous contractions were resistant to tetrodotoxin (10(-5) g/ml) in all osmolalities. In 590 mosm/kg the spontaneous activity had ceased, and a continuous contracture (resistant to tetrodotoxin) was observed with an amplitude of 41 +/- 1% of the maximal response to nerve stimulation at 290 mosm/kg. Similar maximal responses to nerve stimulation were obtained in 260, 290, and 390 mosm/kg. The frequency-response relation in 390 mosm/kg had a leftward shift at low frequencies. In 590 mosm/kg no response to nerve stimulation or acetylcholine was noted, but the preparations contracted vigorously following depolarization with high-K+ solution.
D000818:Animals; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000502:physiology*; D009994:Osmolar Concentration; D011188:Potassium; D051381:Rats; D012996:Solutions; D001743:Urinary Bladder / Q000294:innervation / Q000502:physiology*
D012996:Solutions; D011188:Potassium