Na+ Transport in Toad Bladder Microsomes

摘要: Sodium transport across tight epithelia, such as toad bladder and rabbit colon, is a two-step process originally suggested by Koefoed-Johnson Ussing (1958) for frog skin. According to this scheme Na+ ions diffuse into the epithelial cells, from lumen, through amiloride blockable specific channels are later pumped interstitial space Na+/K+ ATPase. A number of recent studies established fact that apical play major role in regulation transcellular flow sodium. For instance, augmentation aldosterone antidiuretic hormones primarily due an increase density conducting (Palmer et al. 1982; Li Helman 1983). In addition, intracellular feedback inhibition mechanisms were postulated (Schultz 1981) evidence presented permeability coupled internal Ca2+ activity cellular metabolism (Arruda Windhager Taylor 1983; Garty 1983a; Lindemann 1984). Although variations under physiological conditions well documented, molecular mechanism(s) involved these processes not yet clear. The observed may involve one or more following processes: (1) activation preexisting membrane covalent modifications channel protein surrounding lipids (De Lorenzo 1973; Yorio Bentley 1978); (2) noncovalent interaction with cytoplasmic factors, Ca2+,Na+, H+ (Taylor 1979;Frizzel Schultz (3) recruitment subapical vesicles de novo synthesis (Masur 1972;Edelman 1963).