Na Transport across Frog Skin at Low External Na Concentrations

T h e ac t ive t r a n s p o r t of N a across i sola ted f r o g skin h a s b e e n e x a m i n e d extensively, b u t in t h e m a j o r i t y of s tudies t h e o u t e r sur face of t h e skin h a s b e e n b a t h e d w i t h solut ions c o n t a i n i n g re la t ive ly h i g h (115 mM) c o n c e n t r a t i o n s of N a . V a r i a t i o n in ra tes of N a t r a n s p o r t a n d in electr ical p roper t i es of t h e skin w i t h c h a n g e s in N a c o n c e n t r a t i o n h a s also b e e n s tud ied , b u t in m o s t cases c o n s t a n t a n i o n c o n c e n t r a t i o n was m a i n t a i n e d b y us ing o t h e r ca t ions to sub s t i tu te for N a . H o w e v e r , t h e ea r ly d a t a of K r o g h (1) i n d i c a t e d t h a t i n t a c t f rogs cou ld t ake u p N a t h r o u g h t h e skin f r o m solut ions c o n t a i n i n g only 1 0 6 ־ ־ M N a C l . S ince t h e m o d e l of t h e N a t r a n s p o r t system p roposed b y K o e f o e d J o h n s e n a n d Uss ing (2) suggests t h a t N a e n t r y in to t h e skin cells is a