Exogenous cAMP

Glucagon and exogenous cAMP stimulate the Na+-dependent transport of alanine and certain other amino acids into the perfused liver [176] and isolated hepa-tocytes [177-179], There is a rapid initial stimulation of the transport [177, 178] which is probably related to the stimulation of (Na2+-K+)-ATPase activity and membrane hyperpolarization [177], This is followed after 30-90 min by a larger increase which is blocked by cycloheximide [178]. Kinetic analysis indicates that both the short and long term actions of glucagon result in an increase in the Vmax for transport [177,179,180], and it has been proposed that the slower effect is due to the synthesis of a high affinity amino acid transport component [179,180],... 

Shah, D.I. and Singh, M. (2006) Possible role of exogenous cAMP to improve vascular endothehal dysfunction in hypertensive rats. Fundam. Clin. Pharmacol. 20, 595-604. 

It should be possible to mimic the physiological effect of the hormone by the addition of exogenous cAMP. 

Fig. 2. Schematic representation of tests using exogenous ACTH, dbcAMP and pregnenolone (indicated by black horizontal arrows) of the functional integrity of teleost adrenocortical cells exposed to an adrenotoxicant (TOX). A lack of secretory response to ACTH (pattern A, black vertical arrow with X to show disrupted pathways) indicates a general dysfunction of the secretory pathways, possibly involving the ACTH receptor. No response to ACTH but a secretory response to dbcAMP, an analog of cAMP (pattern B), indicates that the steps downstream from cAMP are functional (white arrow bar) but steps upstream are disrupted by the toxicant. No response to ACTH or dbcAMP with a response to pregnenolone (pattern C) indicates that steps downstream from this precursor of cortisol are functional. Note that the concentrations of ACTH, dbcAMP and pregnenolone used in these functional in vitro tests should be physiological rather than pharmacological.

Quantitatively, the binding of Ca2+ to the glycocalyx is of secondary importance compared to that bound by phospholipid elements. The glycocalyx does play a significant role in the determination of myocardial cell Ca2+ permeability (20, 21). Upon arrival of the appropriate electrical stimulus T ction potential), Ca2+ crosses the sarcolemma and is the principal cation responsible for a current called the "slow inward current" (lsi) (3-2, 22, 23, 24). Calcium is conducted across the sarcolemma through channels or pores which are controlled by the phosphorylation of sarcolemmal and sarcotubular proteins. Cardiac sarcolemma and sarcoplasmic reticulum are phosphorylated by exogenous and endogenous cyclic adenosine 5 -5 - monophosphate (cAMP)-dependent protein kinases (25, ... 

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