NEW YORK (Reuters Health) - Because of increased permeability of the bladder epithelium to urinary solutes, potassium (K) levels in urine are lower in patients with untreated interstitial cystitis (IC) than in successfully treated patients or healthy control subjects, new research suggests.

Dr. C. Lowell Parsons, at the University of California San Diego Medical Center, and colleagues theorized that increased bladder epithelial membrane permeability in patients with IC would permit urinary cations to flux more freely across the membrane. As a result, normally high K levels in urine would diffuse into the bladder interstitium, lowering its concentration in urine.

"If K is permitted to penetrate the interstitium, it can cause urgency, frequency and pain through direct nerve depolarization," the authors suggest.

In contrast, sodium (Na) levels are not likely to differ significantly with IC because of its minimal gradient between urine and bladder tissue.

To test their hypothesis, Dr. Parsons' group measured K, Na and creatinine (Cr) in spot urine samples from 37 new, untreated women with IC, 50 women whose IC had been treated successfully for at least 4 months with an oral heparinoid (pentosan polysulfate sodium) and 18 healthy control subjects. They report their findings in the April issue of the Journal of Urology.

K-to-Cr ratios were significantly lower in new patients (0.51 mg/mg Cr) compared with healthy controls (0.88 mg/mg Cr, p = 0.001) and successfully treated (0.66 mg/mg Cr, p = 0.025). Na-to-Cr levels did not differ significantly among groups.

In 24-hour urine specimens from 30 new patients and 47 controls, average K was significantly lower in patients (31.0 versus 46.2 mEq/L, p = 0.01). Again, average Na levels were not significantly different.

"These data support the concept of epithelial dysfunction in IC that results in recycling of urinary K with provocation of symptoms in the bladder interstitium and a decrease in urinary K from normal levels," Dr. Parsons group concludes.

J Urol 2005;173:1182-1185.

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