Interdependence between sodium transport, external chloride, and sodium/calcium exchanger in the isolated skin of the Rana pipiens

The aim of this study was to analyze the relationship of the Na+/Ca2+ exchanger, cytosolic calcium, and chloride to the transepithelial transport of sodium in isolated frog skin. Sodium transport was measured as amiloride-inhibitable short circuit current (SCC). We studied the effect of variations in the concentrations of external chloride and of the manipulation of calcium on sensitive amiloride SCC. Modifications in the movement of Ca2+ were induced by an ionophore, A23187, and a Ca2+ channel blocker, nifedipine. Calcium ionophore A23187 (5 and 20 microM), in a normal Ringer's solution, increased SCC and transepithelial potential difference (PD). In contrast, nifedipine (20 microM) reduced SCC and PD. The role of the Na+/Ca2+ exchanger was studied using dichlorobenzamil (DCB, 50 microM) and quinacrine (1 mM), inhibitors of this exchanger. They selectively increased SCC and PD on the mucosal side of the skin, with no effect on the serosal side. This response occurred only in the presence of extracellular calcium. Replacement of NaCl by sodium methanesulfonate or the addition of furosemide (1 mM) at the serosal compartment, decreased basal SCC and PD and blocked the response to A23187 and the mucosal effect of DCB and quinacrine. These results suggest the presence of an Na+/Ca2+ exchanger located on the mucosal side of the frog skin, which participates in the transepithelial sodium transport. The action of this exchanger may be modulated by external chloride and calcium. J. Exp. Zool. 289:23-32, 2001.     

Renal handling of calcium in hypoparathyroidism.

Treatment of hypoparathyroidism usually requires the use of pharmacological doses of parent vitamin D or near physiological amounts of the hydroxylated metabolites, calcitriol or alphacalcidol. Vitamin D intoxication and hypercalcaemia may be a problem but can be minimised by the use of small doses of vitamin D or its metabolites combined with large amounts of oral calcium. The response to treatment can be easily monitored by measuring serum and urinary calcium and creatinine concentrations. This allows the derivation of two simple indices reflecting calcium load presented to the kidney (calcium excretion in mmol/l glomerular filtrate) and renal tubular calcium reabsorption (TmCa/GFR). These can be used to predict the requirement of calcium supplements and also identify those patients at particular risk of hypercalcaemia.     

Translocation of potassium and sodium in intact maize seedlings

Summary The distribution of K and Na between root and shoot of intact maize seedlings after absorption periods of increasing length up to 24 hours was determined in three series of experiments. In two additional series the redistribution between root and shoot of K and Na absorbed previously during a period of 12 hours was followed up during the next 12 hours. Concentrations were such that either the specific or both the specific and non-specific mechanism of K-absorption present in this tissue were operative.A high degree of specificity in the transfer to the shoot became apparent, the amount of Na transported to the shoot within 24 hours being negligible in comparison to the amount of K transferred within the same period. For the most part this specificity appeared to be due to the fact that the specific mechanism of K-absorption is especially involved in the supply of K for transfer to the shoot. However, non-specifically absorbed K is also liable to transport to the aerial parts at a much higher rate than Na and, in contrast to Na, the translocation of K continues after the plants have been transferred to K- and Na-free media.A scheme is proposed to explain the phenomena described.     

Intracellular calcium handling heterogeneities in intact guinea pig hearts

Regional heterogeneities of ventricular repolarizing currents and their role in arrhythmogenesis have received much attention; however, relatively little is known regarding heterogeneities of intracellular calcium handling. Because repolarization properties and contractile function are heterogeneous from base to apex of the intact heart, we hypothesize that calcium handling is also heterogeneous from base to apex. To test this hypothesis, we developed a novel ratiometric optical mapping system capable of measuring calcium fluorescence of indo-1 at two separate wavelengths from 256 sites simultaneously. With the use of intact Langendorff-perfused guinea pig hearts, ratiometric calcium transients were recorded under normal conditions and during administration of known inotropic agents. Ratiometric calcium transients were insensitive to changes in excitation light intensity and fluorescence over time. Under control conditions, calcium transient amplitude near the apex was significantly larger (60%, P < 0.01) compared with the base. In contrast, calcium transient duration was significantly longer (7.5%, P < 0.03) near the base compared with the apex. During isoproterenol (0.05 microM) and verapamil (2.5 microM) administration, ratiometric calcium transients accurately reflected changes in contractile function, and, the direction of base-to-apex heterogeneities remained unchanged compared with control. Ratiometric optical mapping techniques can be used to accurately quantify heterogeneities of calcium handling in the intact heart. Significant heterogeneities of calcium release and sequestration exist from base to apex of the intact heart. These heterogeneities are consistent with base-to-apex heterogeneities of contraction observed in the intact heart and may play a role in arrhythmogenesis under abnormal conditions.     

Influence of myosin isoforms on contractile properties of intact muscle fibers from Rana pipiens

The myosin heavy chain (MHC) andmyosin light chain (MLC) isoforms in skeletal muscle of Ranapipiens have been well characterized. We measured theforce-velocity (F-V) properties of single intact fast-twitchfibers from R. pipiens that contained MHC types 1 or 2 (MHC1or MHC2) or coexpressed MHC1 and MHC2 isoforms. Velocities weremeasured between two surface markers that spanned most of the fiberlength. MHC and MLC isoform content was quantified after mechanicsanalysis by SDS-PAGE. Maximal shortening velocity(V_max) and velocity at half-maximal tension(V_P 50) increased with percentage of MHC1(%MHC1). Maximal specific tension (P_o/CSA, whereP_o is isometric tension and CSA is fiber cross-sectional area) and maximal mechanical power (W_max) alsoincreased with %MHC1. MHC concentration was not significantlycorrelated with %MHC1, indicating that the influence of %MHC1 onP_o/CSA and W_max was due to intrinsicdifferences between MHC isoforms and not to concentration. TheMLC3-to-MLC1 ratio was not significantly correlated withV_max, V_P 50,P_o/CSA, or W_max. These data demonstrate the powerful relationship between MHC isoforms and F-V properties of the two most common R. pipiensfiber types.

     

Effects of sodium, potassium and calcium on salt-stressed barley

We grew barley ( Hordeum vulgare L. CM 72) for a 28-day period and sequentially harvested plants every 3 or 4 days. Plants were salt-stressed with either NaCl or KCl (125 m M ) with or without supplemental Ca (10 or 0.4 m M final concentration, respectively). We determined tissue concentrations of Na, Ca, Mg, K. S, P, Fe, Mn, Cu and Zn for each harvest date by inductively coupled plasma spectrometry. Uptake (specific absorption rate) was calculated from the element content and growth rates. Salinity had significant effects on the uptake and concentrations of most elements. Mg and Mn concentrations declined with time. The concentrations of all other elements determined increased over time. Element uptake on a root dry weight basis declined with time. Three variables were significantly affected by salinity and correlated with growth; 1) the Ca concentration, 2) the total sum of the cation concentration (TC), and 3) the Mn concentration of the shoot. Salinity reduced Ca uptake and concentrations. Supplemental Ca increased Ca concentrations and was positively correlated with growth during salt stress. Salinity doubled TC, which was negatively correlated with relative growth rate (RGR). Relative growth rate declined at TC values above 150 m M . Salinity reduced the uptake and concentration of Mn. Manganese concentrations in the shoot were highly correlated with RGR. Relative growth rate declined at Mn concentrations below 50 nmol (g fresh weight)⁻¹.     

Migration and Gene Dispersal in Rana pipiens

Although the dominant burnsi gene is widely distributed in Minnesotapopulations of the leopard frog (Rana pipiens) at uniformlylow frequencies, estimates of the effective size of the breedingpopulations suggest that a wider range of gene frequencies mightbe expected due to random genetic drift. Observations of thespring, summer, and fall migrations, however, indicate a levelof migratory activity sufficient to prevent local divergencein gene frequencies. Temperature appears to play a major rolein the springtime migratory and breeding behavior of Rana pipiensin Minnesota.     

Free concentrations of sodium, potassium and calcium in chromaffin granules.

We have measured the contents of Na+ and K+ in isolated chromaffin granules. Total contents varied between 227 and 283 nmol/mg of protein, equivalent to matrix concentrations of 53-66 mM. The value found depended on the isolation buffer used, and the ratio of the two ions reflected the composition of the buffer. We then measured the free concentration of each of these ions, and of Ca2+, in the matrix, by using a null-point method with acridine-fluorescence quenching. This monitored H+ fluxes induced by an ionophore in the presence of known concentrations of the ion in the supporting medium. In contrast with organic constituents of the matrix, which have low activity coefficients, Na+ and K+ were found to have activity coefficients around 0.8 Ca2+, however, was strongly bound: its free concentration was only 0.03% of the total.     

The ear and hearing in the frog, Rana pipiens

The development of electric organ spindles of Gymnarchus niloticus has been investigated with respect to the exact time and place of origin and the process of formation of the adult plan. The results are compared with those of Dahlgren ('14). A common primordium for all the electroplates of of a spindle as held by Dahlgren ('14) is not supported by the present work.