Abstract
Electrogenic cation transport across the caecal epithelium of the leech Hirudo medicinalis was investigated using modified Ussing chambers. Transepithelial resistance (RT) and potential difference (VT) were 61.0 +/- 3.5 omega.cm2 and -1.1 +/- 0.2 mV (n = 149), respectively, indicating that leech caecal epithelium is a "leaky" epithelium. Under control conditions short circuit current (ISC) and transepithelial Na+ transport rate (INa) averaged at 22.1 +/- 1.5 microA.cm-2 and 49.7 +/- 2.6 microA.cm-2, respectively. Mucosal application of amiloride (100 mumol.l-1) or benzamil (50 mumol.l-1) influenced neither ISC nor INa. The transport system in the apical membrane showed no pronounced cation selectivity and a linear dependence on mucosal Na+ concentration. Removal of mucosal Ca2+ increased ISC by about 50% due to an increase of transepithelial Na+ transport. Trivalent cations (La3+ and Tb3+, 1 mmol.l-1 both) added to the mucosal Ringer solution reduced INa by more than 40%. Serosal ouabain (1 mmol.l-1) almost halved ISC and INa while 0.1% (= 5.4 mmol.l-1) DNP decreased INa to 11.8 +/- 5.1% of initial values. Serosal addition of cAMP increased both ISC and INa whereas the neurotransmitters. FMRFamide, acetylcholine, GABA, L-dopa, ...Continue Reading
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