Physiological and molecular mechanisms of inorganic phosphate handling in the toad Bufo bufo

Abstract

The aim of this study was to elucidate mechanisms of P(i) handling in toads (Bufo bufo). We introduced toads to experimental solutions of various [P(i)] and high P(i) diets and measured urine and lymph [P(i)]. Both lymph and urine [P(i)] increased with increasing P(i) loads, indicating P(i) absorption across skin and intestine. An initial fragment of a NaPi-II type transporter was amplified from kidney, and the full-length sequence was obtained. The protein showed the molecular hallmarks of NaPi-IIb transporters. When expressed in Xenopus oocytes the clone showed unusual pH dependence, but apparent affinity constants for P(i) and Na(+) were in the range of other NaPi-II transporters. Expression profiling showed that the transporter was present in skin, intestine and kidney. Reverse transcription-polymerase chain reaction assays on dissected renal tubules indicated expression in the collecting duct system. Collecting tubules and ducts were isolated, perfused and microelectrode recordings showed electrogenic P(i) transport in apical and basolateral membranes. Taken together, our results show that P(i) is handled by intestine, kidney and skin. The presently cloned NaPi-IIb is a likely candidate involved in P(i) absorption across these epithelia. In addition, electrophysiological experiments suggest that the collecting duct system plays an important role in P(i) homeostasis.

Functional characterization of the vertebrate primary ureter: Structure and ion transport mechanisms of the pronephric duct in axolotl larvae (Amphibia)

“…However, in terrestrial anurans, K + secretion through apical K + channels seems a major task of the principal cells [34-39]. In the current study we provide evidence for a principal cell, which has the characteristics of the mammalian collecting duct principal cell, i.e.…”

Processing of naturally occurring sense/antisense transcripts of the vertebrate Slc34a gene into short RNAs

“…2, A, lane 6, and C, lanes 7-9). To test the specificity of the reaction we used homologous sense RNAs from zebrafish (Slc34a2b) and toad (Bufo bufo) (9,20). Both transcripts cross-reacted with the Northern probe, but they have no more than 14 consecutive identical bases.…”

Identification of intestinal phosphate transporters in fishes and shellfishes

“…In future research, it will be important to isolate NaPi isoforms and study the dietary responses. Recently, a NaPi-like sequence was isolated from frog skin [20]. In the present study, intestinal NaPi mRNAs were expressed in fish skin (with scales), although their levels of expression were trace, compared with the levels in the intestine.…”

“…In humans, NaPi-IIb mRNA transcript is detected in the lung, small intestine, kidney, pancreas, and prostate [18,19]. In the toad, NaPi-IIb mRNA is detected in the small intestine, kidney, and skin, but not in urinary bladder by RT-PCR [20]. In the winter flounder, intestinal NaPi-IIb mRNA is also detected but to a lesser degree in renal tubules, but not detected in brain, gonads, heart or renal erythropoetic tissue by RT-PCR or Northern analysis [21,22].…”