Jr. Underhay et Jf. Burka, EFFECTS OF PH ON CONTRACTILITY OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)INTESTINAL MUSCLE IN-VITRO, Fish physiology and biochemistry, 16(3), 1997, pp. 233-246
Extreme acid-base imbalances in salmonids have been shown to impact on
gastrointestinal motility. Changes in pH are known to affect cardiac
and skeletal muscle in fish and mammalian intestinal smooth muscle pre
parations. This study was conducted to determine if the contractility
of rainbow trout intestinal muscle was sensitive to pH fluctuations an
d to begin the investigation into the mechanisms by which pH affected
contractility. Isolated duplicate or triplicate segments of rainbow tr
out intestine were suspended in organ baths containing modified Krebs-
Henseleit solution. The pH was adjusted by varying the concentration o
f CO2 aerating the solution and with HCl or lactic acid. Contractility
was determined as response to the administration of 5-hydroxytryptami
ne (5-HT, serotonin), KCl, and transmural stimulation within the pH ra
nge of 6.3 to 8.5. Optimum pH for proximal segments was 7.85 while the
range was much wider for distal segments. Decreasing the pH with CO2
resulted in a greater inhibition of smooth muscle contractility than w
hen the pH was decreased in 100% O-2 with either HCl or lactic acid, p
articularly when the tissues are stimulated electrically. This effect
was ameliorated as the fish attained sexual maturity, although the mec
hanisms involved were not clear. The Cl-/HCO3- exchanger appeared to b
e involved in recovery from acidotic stress, particularly at pH levels
below 6.5. The role played by the Na+/H+ exchanger is still unclear.
Although contractility was inhibited in the presence of the amiloride
analog EIPA (5-(N-ethyl-N-isopropyl)amiloride), whether the inhibition
was due to blockage of ion transport or to cytosolic effects is yet t
o be determined.