Video enhanced imaging of the fluorescent Na+ probe SBFI indicates that colonic crypts absorb fluid by generating a hypertonic interstitial fluid

Abstract

Extracellular accumulation of Na⁷⁺ detected by video-enhanced microscopic imaging of the impenneant fluorescent probe SBFI[1,2] confirms the view that colonic crypts produce a hypertonic absorbate ca 1000 mOsm·kg⁻¹, thereby generating a large osmotic pressure across the crypt wall. This creates a high fluid tension within the crypt lumen, sufficient to dehydrate faeces [3,4]. When bathed in Tyrode the SBFI·Na⁺ fluorescence indicates a [Na⁺) ca 750 mM within the interstitial space of metabolizing rat descending colon. There is no evidence of interstitial Na⁺ accumulation in octanol (2 mM) or in rabbit colon incubated with 1.0 mM ouabain and no evidence of Na⁺ secretion via the crypt lumen during absorption [5].