Action of forskolin on non-electrolyte permeability across the frog skin as compared to that of vasopressin and isoprenaline

Forskolin, a natural diterpene activating the adenyl cyclase in a receptor-independent manner, increases symmetrically both transepithelial fluxes of urea and erithrytol through the frog skin. The effect is dose-dependent, being 5 X 10(-6) M the dose necessary to obtain the maximal action. Forskolin-induced permeabilization is inversely proportional to the molecular weight of water soluble molecules (urea greater than erythritol greater than mannitol); also the permeability of a mainly lipid soluble molecule, i.e. antipyrine, is slightly increased by the diterpene. The permeability pattern is more similar to that induced by isoprenaline as compared to that elicited by vasopressin. Differently from what occurs in other tissues, small doses of forskolin (10(-8) M) are unable to potentiate the actions of vasopressin and isoprenaline on urea permeability across the frog skin. Moreover, the maximal action of forskolin is not additive with the maximal ones of isoprenaline and vasopressin.     

Effect of vasopressin on the permeability of non electrolytes across the skins of Rana esculenta and Bufo bufo

Maximal doses of vasopressin increase the permeability of the skins of Bufo bufo and Rana esculenta to urea, ethylene glycol, glycerol, erythritol, beta-alanine, leaving virtually unmodified that of mannitol and antipyrine. These results demonstrate that the response to vasopressin is quite different in amphibian skins as compared to the bladders. A careful analysis of the effects of vasopressin on non-electrolyte permeability as a function of their molecular weight demonstrates that hormone elicits the formation of pores with a diameter inferior to 4 A. Under vasopressin treatment the skins exhibit a selectivity for polyhydroxylated molecules as compared to urea and beta-alanine. This selectivity is not due to active of facilitated transport and is not impaired by phloretin or DTNB which selectively blocks the permeability of urea or ethylene glycol in erythrocytes. It is proposed that the site of such selectivity is located in other plasma membranes of the epithelium.     

Prey capture kinematics and four-bar linkages in the bay pipefish, Syngnathus leptorhynchus

Because of their modified cranial morphology, syngnathid pipefishes have been described as extreme suction feeders. The presumption is that these fishes use their elongate snout much like a pipette in capturing planktonic prey. In this study, we quantify the contribution of suction to the feeding strike and quantitatively describe the prey capture mechanics of the bay pipefish Syngnathus leptorhynchus, focusing specifically on the role of both cranial elevation and snout movement. We used high-speed video to capture feeding sequences from nine individuals feeding on live brine shrimp. Sequences were digitized in order to calculate kinematic variables that could be used to describe prey capture. Prey capture was very rapid, from 2 to 6 ms from the onset of cranial rotation. We found that suction contributed at most about one-eighth as much as ram to the reduction of the distance between predator and prey. This movement of the predator was due almost exclusively to movement of the snout and neurocranium rather than movement of the whole body. The body was positioned ventral and posterior to the prey and the snout was rotated dorsally by as much as 21 degrees, thereby placing the mouth immediately behind the prey for capture. The snout did not follow the identical trajectory as the neurocranium, however, and reached a maximum angle of only about 10 degrees. The snout consists, in part, of elongate suspensorial elements and the linkages among these elements are retained despite changes in shape. Thus, when the neurocranium is rotated, the four-bar linkage that connects this action with hyoid depression simultaneously acts to expand and straighten the snout relative to the neurocranium. We confirm the presence of a four-bar linkage that facilitates these kinematics by couplings between the pectoral girdle, urohyal, hyoid complex, and the neurocranium-suspensorium complex.     

Validated age and growth estimates for the shortfin mako, Isurus oxyrinchus, in the North Atlantic Ocean

Age and growth estimates for the shortfin mako, Isurus oxyrinchus, derived from vertebral centra of 258 specimens (118 males, 140 females), ranging in size from 64 to 340 cm fork length (FL) were compared with data from 22 tag–recaptured individuals (74–193 cm FL) and length–frequency data from 1822 individuals (1035 males, 787 females; 65–215 cm FL). Annual band-pair deposition, confirmed by a concurrent bomb radiocarbon validation study, was used as the basis for band interpretation. Validation was further confirmed with a tetracycline-injected male shortfin mako recaptured after being at liberty off South Africa for 1 year and aged at 18 years. Growth rates from tag–recapture analysis (GROTAG) were higher than those derived from vertebral annuli and were only available from sharks up to 193 cm FL at recapture. Modal length–frequency data were used to verify the first four age classes. Growth curves were fit using both von Bertalanffy and Gompertz models. The 3-parameter version of the von Bertalanffy growth function produced the most biologically reasonable values for males, based on observed data (L _∞  = 253 cm FL, K = 0.125 year^?1 (estimated longevity = 21 year), and L ₀ = 72 cm). The 3-parameter version of the Gompertz growth function produced the most biologically reasonable estimates, for females (L _∞  = 366 cm FL, K = 0.087 year^?1 (estimated longevity = 38 year) and L ₀ = 88 cm. Males and females were aged to 29 (260 cm FL) and 32 years (335 cm FL), respectively. Both sexes grew similarly to age 11 (207 cm FL, 212 cm FL for males and females, respectively) when the curve leveled in males and continued to rise in females. Age at 50% maturity was estimated at 8 years for males (185 cm FL) and 18 years for females (275 cm FL). The species grows slower, matures later and has a longer life span than previously reported in North Atlantic waters.     

Mimicry of dimerization by synthetic peptides designed to target homologous regions of proteins

Rapid progress in sequencing various genomes has highlighted the need for the development of biochemical reagents for the detection of thousands of expressed gene products. The magnitude of this detection problem exceeds current technical capabilities. In an attempt to address this shortcoming, a novel approach has been developed called mimicry of dimerization. Peptide tags have been designed to bind to a specific region of parvalbumin on the basis of amino acid sequence homology with this segment. Multivalent ligands were produced by coupling the synthetic peptides to activated dextran polymers and binding was assessed by chemiluminescence of enhanced avidity reactions using a high density of target protein at the binding surface. Binding of the peptide ligands to parvalbumin was strongest under assay conditions that enriched for native monomeric protein and was affected by pH, temperature and solvent conditions. The results suggest that it should be possible to develop specific reagents for tagging proteins on the basis of sequence and secondary structure information.     

Actions of vasopressin and isoprenaline on the ionic transport across the isolated frog skin in the presence and the absence of adenyl cyclase inhibitors MDL12330A and SQ22536.

1. The effects of both adenyl cyclase inhibitors (MDL12330A and SQ22536) have been studied on the ionic transport induced by vasopressin and isoprenaline across the frog skin. 2. MDL12330A inhibits the vasopressin action on the short-circuit current (SCC), confirming that this effect is cAMP-mediated. 3. On the other hand, isoprenaline action on the SCC is unaffected by MDL12330A. However, this lack of effect is not a sufficient argument against the role of cAMP in this action; in fact, as MDL12330A is also an inhibitor of cAMP phosphodiesterase, this action could mask the inhibitory effect of the drug on adenyl cyclase. 4. By using the other adenyl cyclase inhibitor (SQ22536), probably deprived of effect on the cAMP phosphodiesterase, we obtained a strong inhibition of isoprenaline action on the SCC. Thus we conclude that the actions of isoprenaline on the ionic transport across the frog skin are also cAMP-mediated.