Investigations of recent years revealed that isozymes of cyclic-3', 5'-nucleotide phosphodiesterase (PDE) are a critically important component of the cyclic-3',5'-adenosine monophosphate (cAMP) protein kinase A (PKA) signaling pathway. The superfamily of cyclic-3', 5'-phosphodiesterase (PDE) isozymes consists of at least nine gene families (types): PDE1 to PDE9. Some PDE families are very diverse and consist of several subtypes and numerous PDE isoform-splice variants. PDE isozymes differ in molecular structure, catalytic properties, intracellular regulation and location, and sensitivity to selective inhibitors, as well as differential expression in various cell types. A number of type-specific "second-generation" PDE inhibitors have been developed. Current evidence indicates that PDE isozymes play a role in several pathobiologic processes in kidney cells. In rat mesangial cells, PDE3 and PDE4 compartmentalize cAMP signaling to the PDE3-linked cAMP-PKA pathway that modulates mitogenesis and PDE4-linked cAMP-PKA pathway that modulates generation of reactive oxygen species. Administration of selective PDE isozyme inhibitors in vivo suppresses proteinuria and pathologic changes in experimental anti-Thy-1.1 mesangial proliferative glomerulonephritis in rats. Increased activity of PDE5 (and perhaps also PDE9) in glomeruli and in cells of collecting ducts in sodium-retaining states, such as nephrotic syndrome, accounts for renal resistance to atriopeptin; diminished ability to excrete sodium can be corrected by administration of the selective PDE5 inhibitor zaprinast. Anomalously high PDE4 activity in collecting ducts is a basis of unresponsiveness to vasopressin in mice with hereditary nephrogenic diabetes insipidus. Apparently, PDE isozymes apparently also play an important role in the pathogenesis of acute renal failure of different origins. Administration of PDE isozyme-selective inhibitors suppresses some components of immune responses to allograft transplant and improves preservation and survival of transplanted organ. PDE isozymes are a target for action of numerous novel selective PDE inhibitors, which are key components in the design of novel "signal transduction" pharmacotherapies of kidney diseases.

Transient fluxes of intracellular ionized calcium (Ca2+) from intracellular stores are integral components of regulatory signaling pathways operating in numerous biological regulations, including in early stages of egg fertilization. Therefore, we explored whether NADP, which is rapidly generated by phosphorylation of NAD upon fertilization may, directly or indirectly, exert a regulatory role as a trigger of Ca2+ release from intracellular stores in sea urchin eggs. NADP had no effect, but we found that the deamidated derivative of NADP, nicotinate adenine dinucleotide phosphate (beta-NAADP), is a potent and specific stimulus (ED50 16 nM) for Ca2+ release in sea urchin egg homogenates. NAADP triggers the Ca2+ release via a mechanism which is distinct from the well-known Ca2+ release systems triggered either by inositol-1,4,5-triphosphate (IP3) or by cyclic adenosine diphospho-ribose (cADPR). The NAADP-induced release of Ca2+ is not blocked by heparin, an antagonist of IP3, or by procaine or ruthenium red, antagonists of cADPR. However, it is selectively blocked by thionicotinamide-NADP which does not inhibit the actions of IP3 or cADPR. NAADP produced by heating of NADP in alkaline (pH = 12) medium or synthetized enzymatically by nicotinic acid-NADP reaction catalyzed by NAD glycohydrolase have identical properties. The results presented herein thus describe a novel endocellular Ca(2+)-releasing system controlled by NAADP as a specific stimulus. The NAADP-controlled Ca2+ release system may be an integral component of multiple intracellular regulations occurring in fertilized sea urchin eggs, which are mediated by intracellular Ca2+ release, and may also have similar role(s) in other tissues.

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Release of Ca2+ from intracellular stores is a widespread mechanism in regulation of cell function. Two hitherto unknown adenine diphosphonucleotides were recently identified, which trigger Ca2+ release from intracellular stores via channels that are distinct from the well-known receptor/channel controlled by inositol 1,4,5,-trisphosphate (IP3): cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP). Here we review synthesis of cADPR from beta-NAD, its hydrolysis to adenosine diphosphoribose (noncyclic) by cADPR glycohydrolase, as well as our knowledge about the metabolism of NAADP. The Ca2+ release triggered by cADPR, NAADP, or IP3 can be distinguished by the action of inhibitors and by desensitization studies. Evidence now emerges that cADPR synthesis from beta-NAD can be stimulated, at least in some cell types by all-trans-retinoic acid as a first messenger. We then review the properties of cADPR and NAADP as potential second messengers in the intracrine regulation of cell functions. Although their exact role in signaling sequences is not yet known, cADPR and NAADP are likely to play important intracellular regulatory functions, as extensively documented for the process of egg fertilization.

A polyuric syndrome with nephrogenic diabetes insipidus (NDI) is a frequent consequence of prolonged administration of lithium (Li) salts. Studies in the past, mainly the acute and in vitro experiments, indicated that Li ions can inhibit hydroosmotic effect of 18-arginineivasopressin (AVP) at the step of cAMP generation in vitro. However, the pathogenesis of the NDI due to chronic oral administration of low therapeutic doses of Li salts is not yet clarified. We conducted a comprehensive study to clarify the mechanism by which Li administered orally for several weeks induces polyuria and NDI in rats. Albino rats consuming a diet which contained Li (60 mmol/kg) for 4 wk developed marked polyuria and polydipsia; at the end of 4 wk the plasma Li was 0.7±0.09 mM (mean±SEM; n = 36). Litreated rats had a significantly decreased (-33%) tissue osmolality in papilla and greatly reduced cortico-papillary gradient of urea (cortex-43%; medulla-64%; papilla-74%). Plasma urea was significantly (P < 0.001) lower in Li-treated rats (5.4±0.2 mM) compared with controls (6.8±03 mM). Medullary collecting tubules (MCT) and papillary collecting ducts (PCD) microdissected from Li-treated animals had higher content of protein than MCT and PCD from the control rats. The cAMP accumulation in response to AVP added in vitro was significantly (A = -60%) reduced. Also, the cAMP accumulation in MCIr and PCD after incubation with forskolin was markedly lower in Li-treated rats. Addition of 0.5 mM 1-methyl,3-isobutyl-xanthine did not restore the cAMP accumulation in response to AVP and forskolin in MCT from Litreated animals. In collecting tubule segments from polyuric rats with hypothalamic diabetes insipidus (Brattleboro homozygotes) the AVP-dependent cAMP accumulation was not diminished. The activity of adenylate cyclase (AdC) in MCT of Li-treated rats, both the basal and the activity stimulated by AVP, forskolin, or fluoride, was significantly (A --30%) reduced, while the activity of cAMP phosphodiesterase (cAMP- PDIE) in the same segment showed no significant difference from the controls. Also, the content of ATP in MCT microdissected from Li-treated rats and incubated in vitro did not differ from controls. The rate of ['4Cjsuccinate oxidation to '4CO2 in MAL was inhibited (-77%) by 1 mM furosemide, which indicates that this metabolic process is coupled with NaCl cotransport in MAL. The rate of "4CO2 production from I'4Cisuccinate in MAL was not significantly different between control and Li-treated rats. In MCT of control rats, the rate of I'4Cisuccinate oxidation was -3 times lower than in MAL.The rate of '4CO2 production from I'4Cjsuccinate in MCT of Li-treated rats was significantly (A +33%) higher than in MCT dissected from control rats. Based on these results, we conclude that at least two factors play an important role in the pathogenesis of NDI consequent to chronic oral administration of Li: (a) decreased ability of MCI' and PCD to generate and accumulate cAMP in response to stimulation by AVPl, this defect is primarily due...