Calcium transport through the luminal membrane of the distal tubule. I. Interrelationship with sodium

Abstract

Calcium (Ca2+) transport by isolated luminal membranes from rabbit renal distal tubule has been characterized. Ca2+ uptake by these membrane vesicles exhibited saturation kinetics. In the absence of sodium (Na+) in the incubation medium, a low affinity system was observed with a KmCa2+ of 2.83 +/- 0.64 mM and Vmax of 3.03 +/- 0.48 pmol/microgram/10 sec. A second type of kinetics was also detected with a high affinity and a low velocity (KmCa2+ 0.04 +/- 0.01 mM, Vmax 1.18 +/- 0.22 pmol/micrograms/10 sec). The luminal membranes from proximal tubules showed a single system with a KmCa2+ of 0.49 +/- 0.20 mM and Vmax of 1.26 +/- 0.17 pmol/micrograms/10 sec. The presence of Na+ sharply decreased Ca2+ uptake by the high affinity system of the membranes from distal tubules, increasing the KmCa2+ to 0.07 mM +/- 0.01 (P less than 0.01) and decreasing the Vmax to 0.27 pmol/microgram/10 sec (P less than 0.005). This effect of Na+ was concentration-dependent, with a half-maximal effect at 38 mM Na+ and a Hill coefficient of 0.9. In contrast, Na+ had no effect on Ca2+ transport through the luminal membranes of proximal tubules nor on the low affinity system of the distal tubule. The composition of the intravascular medium also influenced Ca2+ uptake by the membranes from distal tubules. Compared to mannitol, trans-Na+ or K+ significantly reduced Ca2+ transport. Finally, cis-K+ induced an increase in this transport. As found with Na+, the effect of K+ was concentration-dependent, with a Hill coefficient of 0.42.(ABSTRACT TRUNCATED AT 250 WORDS)

A Comparison of Sources of Sodium and Potassium Intake by Gender, Age and Regions in Koreans: Korea National Health and Nutrition Examination Survey (KNHANES) 2010-2012

“…반면 혈압에 대한 방어 작용을 한다고 알려져 있는 칼륨은 Na/K 펌프의 활성화를 도와 혈관의 확장을 유도하 고 식염의 과잉섭취 상태에도 Na/K 펌프의 활동을 통하여 나트륨의 배출을 돕는다 [11,12]. 또한 신장의 집합관에서 나트륨의 재흡수를 촉진하는 부신피질 호르몬의 분비를 감 소시켜 나트륨의 체외배성을 돕는 작용을 하기도 한다 [4,13]. 그러나 우리나라 국민의 평균 칼륨 섭취량은 남자의 경 우 충분섭취량의 95%, 여자는 80%에 불과한 실정이다 [7].…”

Roles of ATP and cytoskeleton in the regulation of Na+/H+ exchanger along the nephron luminal membrane

“…Puri®cation of PT and DT was carried out according to our previous description (Brunette et al, 1992). The super®cial cortex was cut into small fragments, washed in Krebs-Henseleit solution (KH) and incubated for 20 min in Dulbecco's modi®ed Eagle's medium (DMEM) nutrient mixture F-12 HAM (Sigma) containing 1 mg/ml of collagenase type V and 0.5 mg/ml bovine serum albumin (BSA).…”

Sodium is the Leading Dietary Factor Associated with Urinary Calcium Excretion in Hong Kong Chinese Adults

“…Sodium (Na) is well known to increase UCa excretion [2][3][4][5][6], possibly because of the effect of filtered Na load on the tubular reabsorption of Ca [7]. Itoh and Suyama [3] also observed this effect even when the other dietary confounding factors were controlled.…”