SUMMARY Cell-attached patches from isolated epithelial cells from larval bullfrog skin revealed a cation channel that was activated by applying suction (−1 kPa to −4.5 kPa) to the pipette. Activation was characterized by an initial large current spike that rapidly attenuated to a stable value and showed a variable pattern of opening and closing with continuing suction. Current–voltage plots demonstrated linear or inward rectification and single channel conductances of 44–56 pS with NaCl or KCl Ringer's solution as the pipette solution, and a reversal potential (− V p ) of 20–40 mV. The conductance was markedly reduced with N-methyl-D-glucamide (NMDG)-Cl Ringer's solution in the pipette. Neither amiloride nor ATP, which are known to stimulate an apical cation channel in Ussing chamber preparations of larval frog skin, produced channel activation nor did these compounds affect the response to suction. Stretch activation was not affected by varying the pipette concentrations of Ca 2+ between 0 mmol l −1 and 4 mmol l −1 or by varying pH between 6.8 and 8.0. However, conductance was reduced with 4 mmol l −1 Ca 2+ . Western blot analysis of membrane homogenates from larval bullfrog and larval toad skin identified proteins that were immunoreactive with mammalian TRPC1 and TRPC5 (TRPC, canonical transient receptor potential channel) antibodies while homogenates of skin from newly metamorphosed bullfrogs were positive for TRPC1 and TRPC3/6/7 antibodies. The electrophysiological response of larval bullfrog skin resembles that of a stretch-activated cation channel characterized in Xenopus oocytes and proposed to be TRPC1. These results indicate this channel persists in all life stages of anurans and that TRP isoforms may be important for sensory functions of their skin.
SUMMARY Blood cell flux (BCF) in the pelvic skin of Bufo marinus was lower than Bufo alvarius when toads rehydrated from deionised water (DI) or 50 mmol l –1 NaCl (NaCl). Despite the lower BCF in B. marinus , water absorption was not different between the species when toads rehydrated from DI or NaCl. When fluid contact was limited to the pelvic skin, water uptake from NaCl was lower than from DI, but became greater than uptake from DI as the immersion level increased. Hydrophobic beeswax coating the lateral sides reduced absorption from NaCl but not from DI. Toads settled into water absorption response posture well after maximal BCF was attained in both DI and NaCl, indicating that the behavioural response requires neural integration beyond the increase in BCF. Water exposure increased BCF in hydrated B. alvarius with empty bladders but not in those with stored bladder water. Hydrated B. marinus with an empty bladder did not increase BCF when given water. Handling stress depressed BCF but increased central arterial flow (CAF), measured using a flow probe around the dorsal aorta. In undisturbed toads, CAF increased with the same time course as BCF while heart rate remained relatively constant, suggesting redistribution of blood flow.
SUMMARY The dorsal lingual epithelium from the tongue of the toad Bufo marinus was mounted in an Ussing-type chamber, and the short-circuit current ( I sc ) was measured using a low-noise voltage clamp. With NaCl Ringer bathing the mucosal and serosal surfaces of the isolated tissue, an outwardly directed (mucosa-positive) I sc was measured that averaged -10.71±0.82 μA cm -2 (mean ± S.E.M., N =24) with a resistance of 615±152 Ω cm 2 (mean ± S.E.M., N =10). Substitution of chloride with sulfate as the anion produced no significant change in I sc . Fluctuation analysis with either NaCl or Na 2 SO 4 Ringer bathing both sides of the tissue revealed a spontaneous Lorentzian component, suggesting that the I sc was the result of K + secretion through spontaneously fluctuating channels in the apical membrane of the epithelium. This hypothesis was supported by the reversible inhibition of I sc by Ba 2+ added to the mucosal Ringer. Analysis of the kinetics of Ba 2+ inhibition of I sc indicates that there might be more than one type of K + channel carrying the I sc . This hypothesis was supported by power spectra obtained with a serosa-to-mucosa K + gradient, which could be fitted to two Lorentzian components. At present, the K + secretory current cannot be localized to taste cells or other cells that might be associated with the secretion of saliva or mucus. Nonetheless, the resulting increase in [K + ] in fluid bathing the mucosal surface of the tongue could presumably affect the sensitivity of the taste cells. These results contrast with those from the mammalian tongue, in which a mucosa-negative I sc results from amiloride-sensitive Na + transport.